Memory overwriting problem in CVS

Hey, I posted about a problem I was having with PHP on Friday; I thought it was something to do with the Zend engine, but now I'm not so sure. The bug appears to be something overwriting memory it shouldn't; I'm getting symptoms such as strings turning into ZZZZ's, string keys in hashes turning into "invalid offsets" etc. etc. I can't boil it down to an exact reproducing script, but I can narrow down the date range a little. It's been hard work with CVS down and I didn't think of getting a snap until a couple of hours ago. The problem seems to have been introduced after snap php4-200106111635 but before CVS as of Fri 15th June. To help pin it down, I am using mbstring, pcre and mysql in the problem pages. I'm sorry but I don't have the time to get more specific than that - the problem has so far cost me too much time (but I'm not complaining). --Wez.