If an element is at the end of a priority segment and compare_func returns TRUE, we end up with a mismatch between the priority segment iterator and the list iterator. This can potentially corrupt the priority queue.

What happens is the following:

1.- Before calling compare_func we do:
	GList *elem;

	elem = list;
	list = list->next;

2.- (compare_func) (elem->data, compare_user_data) returns TRUE
3.- If elem is at the tail of a segment then we do:
	segment->last_elem = elem->prev;
At this point we can be sure that 'list' point to the head of the next priority segment (if there is one)
4.- The segment iterator remains unchanged

So what happens next is that from this point on we compare list elements to a segment we've already gone through. So none of the elem == segment->* will ever be true.

I just found this bug recently, I haven't really found the functional impact of this behaviour.