SpellCheck: keydown is not handled sometimes

Problem:

• Sometimes the SpellCheck does not start the event-handler after a keydown.
  (Starting the SpellCheck with F7 works as expected. Only the keydown-handler is not even called.)

Try with:

• TrackChanges on.
• A. open a task, edit an empty segment, don't save it, close the task
• B. open another task, edit a segment with content, don't save it, close the task
• A again
• B again
• ... Sometimes the error occurs, sometimes not. (Even IF it occurs, no errors are noticed.)