When yiz insert a keyframe (on a location keying set f.e.) in the 3D-view and you got an action editor open then the action datablock is not changed (displaying only the button "new") until you hover the action editor with the mouse.
Added a handler in the action_header_area_listener to handle this case
If non-obvious, some technical note about what the cause of the bug was and
how it was solved.
fa88c7ffae