A: When you're a moron and didn't install CF 9.0.1 properly.
I was working on some caching additions to an application when I noticed that using the expireURL attribute was not working correctly. It was removing the URL caches one at a time instead of removing them all. That made no sense to me because after reading Aaron West's blog tutorials on CF9 caching I knew CF 9.01 had fixed this.
An email to Aaron to try and troubleshoot this received a reply to check the version of my CF server. So I did. And it was still CF 9.0. Apparently I didn't do my upgrade properly way back when, and all this time I thought I had been developing on CF 9.0.1.
Don't I feel stupid.