Actually, the behavior is "correct", in the sense that it's working as configured and expected. 

GN doesn't know about mb_config.pyl or that the GN args for the build have changed, so it thinks nothing changed. To deal with that, we list //tools/mb/* in //testing/buildbot/trybot_analyze_config.json , and *after* we run analyze, we check against the whitelist in that file, and if we get a match, we ignore the results of analyze and run everything.

However, in this case the bot isn't actually configured to do anything (no compile or test targets), and so it (correctly) didn't do anything :).