isearch problems

I did some debugging of the isearch problems which I am now reasonably able to reproduce. When the problem occurs search-ring does not get updated - hence why re-searching always uses the previous match. The weird thing is that if I put debug (a message saying what was saved) in isearch-update-ring and eval it the problem goes away. So I'm wondering whether there is some sort of race condition or byte-compiler problem. Also the weird thing is that when the problem occurs there is a message that flashes up before "Isearch: whatever" which I can't read. I'll see if I can debug some more but its very difficult to pin down. andy