I have the same problem. We user version 7.1.0.1337
In a package we have an associated array variable of type:
TYPE my_visit_array_type IS TABLE OF NUMBER
INDEX BY VARCHAR2 (10);
When trying to debug the variable using right click "View Collection Variable" nothing happens. When I do "Add Variable to Watches" it gets added and as value just shows (Collection). When I click on the "..." field there a Text Editor window opens and in it again just the text: (Collection).
I also remember that it worked watching collection variables in debug in the previous version. Hope that helps to sort out the problem.
Best Regards,
Berny