I was very surprised to read in this thread that (apparently) DL passengers sometimes find themselves arriving at a different terminal at LHR to the one scheduled. The poster suggests this isn't a matter of planned terminal moves but on-the-day changes due to aircraft usage.

I've never heard of this before. If an aircraft needs to park somewhere else I'd always expect either (i) the aircraft would be towed after deplaning or (ii) passengers would be bussed to the right terminal from wherever it was parked.

Has BA ever been known to drop passengers off in the wrong terminal?