Explanation of the 4♦ bid is appropriate. It essentially says it's a cue bid showing first round control of diamonds.
This seems particularly bad here because the 2♠ bid marginally agrees hearts. The simplest sort of heuristic here would solve the problem. If GIB doesn't recognize a bid and there is an agreed upon suit, rather than passing, it should just make a minimum bid in the agreed suit. 1X=2X, 1X=3X, 1X-1Y-2Y, and 1X-2Y-3Y all come immediately to mind. Just set a flag in these few situations indicating that X is the agreed suit and if GIB thereafter runs into a hole in its bidding database, DON'T PASS!