I'm on k2 and when I create a new item and put my content and then i upload the "article image" via image tab of K2 sometimes it shows up as popup when the article is opened on front-end, without a close button!

I even have a k2 user module with a "create new item" menu item that shows up as a popop on front-end :ohmy: !

This most likely a conflict with your template's scripts.

Some templates do not support both K2 and Bootstrap. In either way please send a link to the issue, since it is impossible to tell without a live link.