Yes it using Joomla!'s default modal (MooTools Squeezebox).
Bootstrap uses the .modal class as well for its own modal which has different styling. This is causing the conflict.

You can change the modal in your overrides, but if I where in your shoes I would use the CSS solution instead.

Thanks Krikor!
I also would prefer to use the custom.css to overide, but I need to figure out what the change should be. Now with the changes I posted earlier, the editor box does not open in the modal popup window and the Close button does not function.
I don't know if I mentioned that I am using Joomla 3.3.6 and K2 2.5.9.
I know that both of these issues are frequent topics on a number of forums, so a lot of people have the problem. It would certainly benefit the community as a whole if the framework developers stayed consistent with some of the Joomla core functions, OR k2 not use a modal window for the editor and then we avoid the whole conflict.

K2 uses the modal window beacuse it is also compatible with 1.5 and 2.5. Furthermore it is a native Joomla! element.

Normally this is a template issue, since it works on default K2 and the majority of the templates. Send me a link to see what I can do.

I switched to a different template using the Vertek framework (this particular issue is on a BS3 template) and generally everything works as it should. I do not need a modal override in the custom.css and no other hacks for this particular problem.
I also tried a T3 template from another developer and it also works, but with the modal override. I believe that T3 is still based on BS3 framework.
K2 works with no issue on the base Protostar, which is a Bootstrap template. So the issue is with this particular template developer and it is really up to them to address the problem.
But in searching for the solution, I see that this is a pretty common issue, mostly with the BS3 based templates (I have also seen it on some T3) so it is likely coming from those developers that feel that they must somehow use a different modal method for their product for other reasons and K2 support is just an afterthought for marketing. They must not be testing the templates for full K2 function or they would have discovered the flaw and corrected it.
My suggestion, for what it's worth, would be for K2 to abandon the modal window for the front end edits and just use a standard editor page that works under the core Joomla. While not so trendy, it is more universally functional and when the users are doing article edits on the front page, function is more important than form.

Thanks for your kind offer to assist, Krikor, but it is really the responsibility of the template developer to address this (besides-I am working on this on my localhost before taking it to the live site, so linking in from the outside requires more server and router setup than I want to do at this point) .
I appreciate all of your input and support so far and if they provide a solution that might benefit the community as a whole, I will come back and share it. As of now I can proceed with the rest of the site development with what I have. It is not as aesthetically pleasing as the template I wanted, but will be a good second choice.

If I may make a suggestion for the forum here, with template issues like this becoming more common, a section on template issues might be of benefit and could consolidate users searches for specific template problems and solutions. Just a thought.

K2 works with no issue on the base Protostar, which is a Bootstrap template. So the issue is with this particular template developer and it is really up to them to address the problem.

I agree with you.

Thank you for kind words Gary. The default modal cannot be dropped in the current version since it is designed to support Joomla! 1.5 and 2.5 as well.
Starting with the upcoming v3 where support for older versions is dropped, this modal will be gone.

Finally thank you for your feedback.
The template issue is indeed a gray area for the enduser but since users have paid for a specific template and support is only provided to paying members (template club subscribers) it would unethical to provide support for someone else's commercial product.
Another point would be since another dev built it, there is no way of telling which methods they used.

Just thought I'd poke my head in quickly as this thread came up as talking about Joostrap and Bootstrap3 templates ... and this modal issue.

Basically, as stated earlier in this thread, K2 uses a core MooTools modal to support Joomla 1.5 and 2.5 - using an open "modal" class.

I understand from other threads that this is going to change in a coming version of K2, which along with other classes will be extensions specific (more like k2modal) and as Joomla is/has removing updates and support for Mootools, Joomla 1.5 and 2.5 similar would be expected from extension (and template) developers.

Importantly, "modal" is a standard class in Bootstrap 2 AND 3, used (and reserved) by Bootstrap ... nothing done by template developers ... this is a Bootstrap thing. Important to note is that prostar uses modified bootstrap files and is not completely bootstrap compatible ... maybe to try and support Mootools ... but that is to be completely removed from all core functionality and has been getting removed more and more on each core release. The sooner mootools is completely removed from core the sooner a lot of these issues will go away.

There's a few other posts about similar on the K2 forum ... the updates in naming, removal of mootools usage and compatibility with standard Bootstrap (2, 3 and future) will make things much smoother .... and as Krikor said:

Starting with the upcoming v3 where support for older versions is dropped, this modal will be gone.

In at least this instance it is something that the template developer is doing differently. I switched to a different template from another developer also based on BS3 and the modal window works as intended with no hacks. It seems to be in how the CSS files are being used by the developer to create the pages and the modal operation. I have found this issue repeatable in numerous templates all based in some fashion on BS2 or BS3. While the modal class in the base Bootstrap may use the core Joomla functions, developers are doing different things with it to suit their needs and in the process, it is not working with K2. However, they promote the template as K2 compatible, but in reality it is not. If they had fully tested it, they would know it does not work and would (hopefully) fix it. And there lies the rub!

I agree with Gary, It might be a reserved class but you can add a couple of CSS lines to make it compatible with extensions that use Joomla!'s (older) standard modal.