Posted here because this is where ah was told after the fiasco of last time, just thought to post here so that someone who is already registered to view the Bugbase can make a report
Yep, looks like one of the syncs broke the descent code. When you descend it says, "we're heading for this ground co-ord" but then the other bit of the code goes "what, your not on the ground, how can you have a ground co-ord! Break!". Also means Clarr's unit tests didn't catch it to avoid it when syncing. SO we know the problem, and the coders will be looking at it to fix it ASAP.