Good time!
To upgrade to Joomla 3.4.5 (it was 3.4.1) and the values are no longer stored in additional fields k2 editor JCE (not insert images, etc.). It does not work only in the extrafields .
  TinyMCE is working fine but the JCE - not.
Can someone tell me in what side to dig?
k2 2.6.9
JCE 2.5.11

Are you getting any JS errors in your browser's developer tools?

I have 2 warning after choose Tab additional fields:
'webkitMovementX' is deprecated. Please use 'movementX' instead.
'webkitMovementY' is deprecated. Please use 'movementY' instead.

when editing
1 warning
KeyboardEvent.keyLocation' is deprecated. Please use 'KeyboardEvent.location' instead.

click Save
Uncaught TypeError: Cannot read property 'getBookmark' of nulll.add @ index.php?option=com_jce&view=editor&layout=editor&task=pack&component_id=820&wf1926ed1705ae2320464…:2d @ index.php?option=com_jce&view=editor&layout=editor&task=pack&component_id=820&wf1926ed1705ae2320464…:2tinymce.create.dispatch @ index.php?option=com_jce&view=editor&layout=editor&task=pack&component_id=820&wf1926ed1705ae2320464…:2k.create.save @ index.php?option=com_jce&view=editor&layout=editor&task=pack&component_id=820&wf1926ed1705ae2320464…:2(anonymous function) @ index.php?option=com_jce&view=editor&layout=editor&task=pack&component_id=820&wf1926ed1705ae2320464…:1220tinymce.create.dispatch @ index.php?option=com_jce&view=editor&layout=editor&task=pack&component_id=820&wf1926ed1705ae2320464…:2c @ index.php?option=com_jce&view=editor&layout=editor&task=pack&component_id=820&wf1926ed1705ae2320464…:2j @ index.php?option=com_jce&view=editor&layout=editor&task=pack&component_id=820&wf1926ed1705ae2320464…:2y @ index.php?option=com_jce&view=editor&layout=editor&task=pack&component_id=820&wf1926ed1705ae2320464…:2e.submitform @ core.js:1window.submitform @ core.js:1Joomla.submitbutton @ index.php?option=com_k2&view=item&cid=50:210onclick @ index.php?option=com_k2&view=item&cid=50:332

This error is coming directly from JCE. You need to address this issue to the JCE developers.

found in what was the problem!
disabled JA K2 Filter and all was ok!

Thanks for sharing that.