It appears that
tinymce puts its plugin displays (and so their subordinate fields)
into a div peer to the original (and parent) blockUI div that the main
tinymce editor is in. This means that the plugin becomes out of
the context of the blockUI div and so is treated as part of the
overlay where keystrokes are trapped/bound.
One solution would
be if blockUI allowed a callback in the internal 'handler'
function other than just for targets with class
'.blockOverlay' (which is what the callback
'.onOverlayClick' is limited to).