If Piwik is load balanced between 2 servers, and administrative calls are done on serverA and serverB hosts the UI. When serverA has modifications to Goals or websites, causing tmp/cache/tracker/ to be deleted and rebuilt, this is not done in serverB until the next cache expire.
Therefore the Piwik UI must never rely on the tracker cache. It makes sense but for "performance" reasons it was done. Now, we will have extra SQL requests on a few requests to the UI, but shouldn't impact much.