Commented by: @hvlad

There is no need for bugcheck, engine should handle in-limbo transactions in the same way at all places:
raise error or work as if transaction is active (if isc_tpb_ignore_limbo was specified).

Patch for V4 implements this strategy.

Patches for v2.5 and V3 still not check isc_tpb_ignore_limbo in prepare_update but now raises isc_rec_in_limbo
error instead of bugcheck, allowing all connections to continue work with database.