After collecting enough diamonds in this cave, the exit does not open.
A quick check reveals that this is because this cave set (stored in GDS binary file format) uses the PLCK game engine (first few bytes of the cave set file are "GDashPLC"), which (as the only engine of all GDash engines) unsets the flag "border_scan_first_and_last" (which is set for all other engines).
This means that the first and last row of the cave (with the exit element stored in the first row in this case) is never scanned, which means that the closed exit will never be changed to the open exit if the required number of diamonds was collected, effectively rendering this cave unsolvable.
So there is the suspicion that this cave set was maybe incorrectly converted from the original C64 game.
Has anybody else an idea what might have gone wrong here, or what else could be checked?
A quick fix seems to be converting this cave set to BDCFF format (which always sets this flag), but this may break other things in a subtle way...