Joomla K2 frontend sbox-window from my point of view has a bug.
Problem
If you open for modification a K2 item in frontend, it presents only 2 buttons on right top SAVE and CLOSE:
If you Save it doesn't close, if you Close it doesn't save without any warning! It is very dangerous and you can loose a lot of work.
Possible Solution
Joomla Article frontend modification has a very simple solution :
Still 2 buttons, but with a different use: SAVE & CLOSE and CANCEL.
Best solution
Anyway I would prefer the solution used both for Joomla Article backend and K2 Item backend:
3 buttons, SAVE & CLOSE, SAVE only, CANCEL
What can I do ?

Let me know what I can do to improve that.
Thanks

There are extension which extend K2's frontend editing functionality.
You can look for one in the JED.