Try the following using Tk 8.6b3 (Tk-Cocoa) on OS X (happens in OS X 10.7 and 10.8 at least). This works with any of the wish menus apart from the "Wish" menu itself:
1. Launch wish
2. Select one of the wish menus and see that the items are enabled
3. type into the console: "tk_chooseColor"
3. while the dialog is open: select one of the wish menus and see that the items are disabled
4. dismiss the color dialog
5. select one of the wish menus and see that the items are still disabled
At step 5, the menus should be enabled again, but they are not. If you do the same sequence but skip step 3, then everything is OK. So it seems that choosing a menu while a modal dialog is open will correctly show disabled menu items but the menu will never be re-enabled afterwards.
This happens not only in plain wish but also with custom menus from [. configure -menu]