[susan53]

Either it was an activity specifically on creating defining relative clauses, where you were told to embed the first proposition into the second (which doesn't mean it can't be done differently, only that you were practising one specific grammatical point rather than another - and doesn't any way explain number 3 which is actually a non-defining relative clause), or it failed to take context into account. In this situation (the man wh stole the money) it's true that the defining clause would be much more likely in most contexts. But consider eg a context where the man was poor and had no money to feed his children :
The man, who must still be punished of course, only stole the money because his children were hungry.

We still have the basic structure : The man, who must ... be punished ..., .. stole the money... The adverbials of course and only are irrelevant to the basic structure, as is the added subordinate clause starting because.
So there's nothing ungrammatical about it.