I looked into that windows build and sourceMappingURL in failed tests looks like this (note mixed slashes):
The problem is in existing code using util/path, which is OS-dependent and produces back slashes under Windows, my patch didn't modify that code branch:
I guess we have two possible resolutions:
1. leave existing behavior as is and make my tests accept mixed slashes
2. newly use forward slashes only, leave my tests intact and announce it as a potentially breaking change in next release
Solution 2 is better way forward IMO. I believe mixed slashes work because browsers are forgiving and treat backslashes as forward slashes in source mapping resolution. This change would have some tiny chance of breaking existing code with would depend on specific way how clojurescript generated sourceMappingURL with backslashes up until now.
I will leave it for your consideration. And then move forward with your decision.