Well, I have heard it has happened on the E145s before but only on this forum........I personally have never 'come across' any problems with fumes on the now Flybe E145s.
One would think however that had it been fumes, the crew and engineers would have known it. The smell was unusual and not familiar so the crew decided it best to return to BHX as a precaution. Not sure why oxygen was used - I suppose this is standard in these situations.