Although this bug seems to be fixed for an instructor, the current view for a student after an assignment has closed needs repair. (I've submitted a followup comment to the bugzilla item cited by Mike.)
During an office visit last week, I noticed a student was not seeing the SOLUTION link/popup after answerDate until CheckAnswer had been invoked. I think this temporary hiding of a Solution (at a time when it should be obviously available) is wrong.
After an experiment with one of my pseudo-student accounts, I can confirm that unfortunate behavior. It is independent of the student's status for work on a problem: 100% or (partial correct) or (all wrong) or (not attempted). Previous behavior (after answerDate) required CheckAnswer after selecting the ShowSolution checkbox --- that awkwardness is better than current hiding of Solution availability until the CheckAnswer button is used.
PS: after this is fixed, I suggest ShowAnswer for a student after answerDate be handled with a similar link/popup. That would better emphasize the value of CheckAnswer for a student continuing to work on a problem. OTOH, since CorrectAnswers and Solutions are now shown using drastically different mechanisms, I would be content with a fix of the wrongly delayed display of Solution link/popup.