My 24-Sept-2013 comment for
described this bug (including the fact that it does not appear when an instructor is "Acting As a student").
You can view my contemporaneous Bugzilla report using URL
My 7-Oct-2013 post at
describes what I have done as a crude substitute for a fix.
FWiW: merely clicking on "Check Answers" is sufficient to expose the link to Solution, entering an answer is not required. If the problem displays a "Get a new version" button, then clicking on it will also expose the link to the Solution.
OTOH: displaying another problem and then returning to the problem will require yet another "Check Answer" click before its solution can be displayed again.