Yes it sounds dodgy;
In my opinion, the only absolutely safe way to proceed is to obtain clarification from the planning office. If they say (in writing) that they do not regard the occupancy clause as continuing to have effect, fine. Otherwise I would not buy.
However, I should also say that there are many people who would still buy, as there seems to be absolutely no enforcement whatever of occupancy clauses. Also, some solicitors seem happy enough to act in these purchases -possibly due to perceived legal defects in the validity of the occupancy clauses (I regard this argument as weak, which is why I refuse to act in these transactions, but I must acknowledge that it is possible for a colleague to differ in good faith).