A bug (at least under X-Windows) is that after a while (a certain number of paste actions?,
a certain elapsed amount of time?, pasting from certain windows?, ...),
you can not paste anymore to Emacs. Either only the last entry you had in the paste buffer before it went 
wrong can be pasted, or nothing at all. Copying and pasting between ACEDB windows is not affected.
Copy and paste within Emacs is not affected either. In this state both programs have their
own independent non-interchangeable paste buffers.
Quiting and restarting either ACEDB or Emacs seems to be the only way to "reset" the situation.

Laurens