Hi folks :) I sent this message to the xml@gnome list, but that place is seems very quiet lately. I'm hoping someone here might have some insight. Indeed this might be a bug in lxml, we're not sure. Background: We use libxml and libxslt in one of our applications (specifically, in Python via lxml). Recently we've seen our application dying at strange times for no apparent reason. We managed to get a core file out of one crash, and the results of some of our debugging are here: http://xml.pastebin.com/m70c259d6 (I'd be happy to poke more in a particular direction on there, I'm a bit new to gdb :) To me, it seems the parser is complaining while trying to parse the namespaces in the <stylesheet> node in transforms/_base.xslt The node for that opens like this: http://www.w3.org/1999/xhtml"; xmlns:xsl="http://www.w3.org/1999/XSL/Transform"; xmlns:tfxslt="http://tfnet.co.uk/ns/tfxslt"; xmlns:fb="http://www.facebook.com/2008/fbml"; extension-element-prefixes="tfxslt str exsl" exclude-result-prefixes="str exsl tfxslt fb" xmlns:error="http://www.woome.com/error/";> I dug a little deeper and found a bunch of the "address out of bounds" errors and thought I should ask here as I'm drawing a blank on where to go next. The problem happens intermittently, but usually several times a day. I could probably reproduce it. I also see the 'exclude-result-prefixes' mentioned in the backtrace, could that be involved here? Any suggestions you have would be much appreciated!