We have the same challenge for designing our homework assignments but it isn't a new problem or a problem in MapleTA for us.  All MapleTA does is save them the trouble of typing the question, they could use something like wolfram for any assignment we can think of that coveres the same material.

How did you handle this for paper based assignments?

As for our proctored test center we simply block access to web sites that aren't whitelisted.

In MapleTA you have the ability to proctor assessments so that they require someone to authorize their start and end.  This proctor ensures that the students don't cheat.

Whether it is Wolfram or a textbook or simply a friend who has already completed the assessment there are many ways a student could avoid having to do the work themselves.  The only way I know to get around that is a proctor.

With tehcnical support's help I was able to get this working.

For others who might have this problem, the field which was missing from our database was ALLOW_SELF_REGISTRATION which could be set to true or false.

We've had similar frustrations and the nickname "Question Supository" was coined by one of our faculty members has started catching on!

The good news is that in MapleTA6 all of our major complaints in this area have been addressed, the Question Repository is much improved.  It doesn't do everything we'd like but the nickname no longer applies.

If you are able upgrade to version 6, otherwise you may want to see if you can go to version 4.  Given our trouble with version 5 I would have preferred to run the fully hotfixed version of 4 until 6 became available.