Strange Apache Segfault caused by XDebug

Strange Apache Segfault caused by XDebug

I've got a quite large codebase (nothing too massive though) that is
encountering a segfault on the one of the most innocuous lines of code
ever.
Basically this (within a class method):
$this->saved = $saved;
gettype() confirms $saved is a boolean, and it's defined in the class as
protected. If I comment it out it runs fine.
Since I disabled XDebug it's started to work, but I can't really get any
work done without XDebug. Any ideas on what it could be and how I can fix
it?
Thanks!