Whilst having to debug this is still undesirable, I recommend trying `rr` (http://rr-project.org/) to track this if you're ever in such a situation. It's as simple as setting a watchpoint and reverse-continue-ing!

I don't do much C/++ these days, but when I do (and it's a large codebase which is hard to debug), `rr` is invaluable. It works with Rust too.