I broke them when I added the data url test in r34504. I think the issue is the result is getting cached and the test is seeing the response from the other test.
Created attachment 21655 [details]
I can't reproduce this on my machine, but this should bust through the cache, if that's the issue.
Created attachment 21656 [details]
As Maciej suggests, using the Cache-Control: no-cache header is a better way to prevent caching.
Comment on attachment 21656 [details]
Turns out we needed no-store in the Cache-Control header as well.