java Preview reverts to Interface definition

[buggyfunbunny]

(12.0.2 xp)

This is strange.  The Preview is set in Quick Filter/Show All Tags.  Putting the cursor on a method shows the Interface definition in Preview, not the concrete class method. 

If I go to Project/Project Properties, the Preview window displays the concrete method for as long (plus a few extra seconds) the File list is up.  Closing the window reverts to the Interface definition.  Similarly, if I delete and rebuild the tag file.

If this isn't a known issue (either in my configuration or SE), I'll send the screens shots to Support.

[buggyfunbunny]

Support already sent back an email (kudos).  Got me doing some stuff.  Whereupon I noticed that:

private FooBar fooBar = null;

at the top of the file (FooBar being the Interface).  Then

fooBar = new FooBarImpl();

just before where I was working, then

fooBar.someMethod().

Changing the define to

private FooBarImpl fooBar = null;

And it works fine.  Now, this sounds familiar, in a back of the brain stem sort of way.  But this is permissible syntax, and the tagger should show the real method.