While doing load tests we noticed that ab was hitting this condition and not being cached. Apparently it is including some POST data in the GET request (maybe just some white space or newline?)
It seems to me that batcache should only be caching GET requests anyways. So this commit just checks the request method.
Could you post the full HTTP requests that are hitting this condition?
Also if you could inspect the variables in that test, it would help in narrowing down the cause of this.
Closing this request as no further data was provided and it's not clear how to reproduce this.