i assume that you had either Tier1 or 2. did your BRP replacement visa had a note on it saying that "employement prohibited" ? did you not work when you got back to the UK until the card was reissured ?or did you (or your employer) confirmed via UKBA that your right to work is not affected...

what happened afterwards ?
did you use the libk ?
had they given you a clearance to work while your card is reissued ?

i am at the same situation.
therefore i would really help to hear what happened in your case ?