Hrm. Makes sense. However, I just thought of something. There were two expressions like that, and while the first one had trouble, the second one didn't. That is, I didn't have to group the " on the second expression.
The second one was at the end of the expression - if it had matched the zero
width alternative then the overall match would have been shorter.
Here's another alternative expression that I think does what you want:
const char* badPatternStr = "