Document is not public. So some comments:
Some items from the context menu didn't do anything (View Type Hierarchy called on function),
so maybe they should have been disabled.

Type hierarchy can be showed for a class or structure.
Unfortunately time of detecting object under cursor is too large.
It make a showing pop up menu too slow.
So now it is impossibles hide/gray this menu item.

See java editor. It also do not disable items in context menu.
It should be common multi language solution:
1 variant: item disabling should be very fast or do not disable item
2 variant: do not disable items

Determining whether these items are applicable takes too long to be done in the UI thread.

So the best we can do is provide a message in the case they aren't 
(instead of just doing nothing silently).

Stepan, do you agree?

Determining whether these items are applicable takes too long to be done in the UI thread.

So we have two options:
1) Leaving it as it is (which is quite consistent with Java)
2) Displaying a message in the case the action isn't applicable
(either in the status bar or in dialog - I believe status bar is preferrable)

I strongly disagree that such defects are really P2.

According to netbeans quidelines
http://qa.netbeans.org/bugzilla/bug_priority_guidelines.html
it isn't more than P3:

> P3:
> Highly visible usability problem

I close bug because "Type Hierarchy" shows message in the status bar.
I think that solution with message dialog is not user friendly.
So there are no another "appropriate" solution for problem.
I close as invalid.