This has actually come up more often than I thought it would. If someone renames or deletes a test that failed in the last build, the next run of smokeFailingTests will always attempt to rerun the test, even if it no longer exists:

http://buildbot.mongodb.org/builders/Windows%2064-bit/builds/4695/steps/test/logs/stdio

The only way to correct this right now is to log on to the build machine and delete the fail.smoke file by hand.