Before I report this a (yet another) bug. Is anybody else experiencing this?
If you have a class marked composite (and therefore with an associated diagram), when you make the class an AssociationClass via
<vertex context menu>|Advanced[ch9658]|Association Class..., the composite setting is
removed.
AND... (to add insult to injury)
when you put the "composite" setting back, the:
<vertex context menu>|Advanced[ch9658]|Unlink Class and Association,
disappears to be replace by:
<vertex context menu>|Advanced[ch9658]|Association Class...which menas you can't unlink the the two. Never mind the fact that on the diagram, the rendering clearly shows it's an Association Class, the menus don't.
THEN you discover that the Association won't select consistently!
ANDsince there isn't a means to unlink the Class from the Association from the <edge context menu>, you're left up the creek without the proverbial paddle!
This is EAUI of the purest form... 
Now lest my fellow users think I'm being too harsh... I'm NOT finding these
wierd bugs by rigourously testing this product. I'm just trying to use it to do my real job - Data Architecture! (By the way I'm using IE notation on the diagram)
EA SERIOUSLY reduces my productivity over what it should be!If there was anything better than EA out there I'd switch in an instant! It is a sad indictment on our industry... (You might gather I've had a tough time with EA this week - I actually started to
use it again...)
Paolo
Using EA in spite of EA not because of it... 
Caveat - it may be that this is happening ONLY on my machine (hence the question at the start). In which case I plead that the observed behaviour is only slightly stranger than the already admitted inconsistencies in EA!