Kirk,
Well, this is embarrassing. I figured it out, at least in my case: User error. I didn't have the "Add/Modify" check boxes checked for my catalogs. The menu items were disabled because there were no modifiable catalogs active. (I assume that's the intent.) I think part of the problem is that the disabled items in the contextual menu don't look disabled (e.g., they look more white than grayed out), so it never occurred to me that they were not clickable and that "abled" items should look bold.
Sorry about the confusion. But it does make me wonder what issue you reproduced with Apple Magic Trackpad, and what exactly you "fixed" with the new build. And I wonder what Soizic's problem was too. Was there an actual coding issue (and my user error was just a complicating factor)?
Now that I (think) I know how this is supposed to work, there might be some other usability issues/conundrums related to how/whether to disable all the contextual menu items. For example, since Collections can be empty before adding images, why disable the Create Collection menu item(s) at all? (That's just one example. I'll have to play with this more before I document a full list of issues.)