I found a similar issue regarding an 'isdigit' call:
https://connect.microsoft.com/Visual...debug-compiles
In particular:
"The assert ensures EOF (-1) and the values representable by an unsigned char (0 to 0xFF) are the only values allowed as input to this function. To ensure the implicit cast to int results in a valid value, be sure to cast char values to unsigned char."
I'll push a fix for this..but, we may need to keep an eye on future crashes - if it is relevant.
EDIT: Ok, pushed a fix for this particular case. If you run across any more, or if this causes issues, please post back.