The html lexer is crashing given the attached mako file. The problems seems to be with the text: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
I think what's happening is that the < is colored as an operator, setting the startSeq to 23 (given the file) and then the block for a SGML DTD is hit and styler.ColourTo(i - 2, StateToPrint); is invoked. i - 2 is 21 and the assert in ColourTo fails. I'm also seeing a segfault in non-debug mode and can get a backtrace for it if you need it.