Er I guess to better phrase I'm certain it's an issue related to wxWidgets, not with wxWidgets itself. But anyway, I can't seem to come up with a reliable way to crash it.
I tried creating a small project to try and replicate this issue in a simpler environment and haven't been able to yet. I think it might just be because it's hard to do. My theory is that since the code completion seems to require at least 3 letters to start working that it just simply requires incredibly fast typing to make the tooltip for function arguments and the tooltip for code completion happen at the same time to cause a crash.
I wish I could come up with a more reliable way to crash it. Sorry about that :/