This is shortsighted design for a cache. Thankfully (and partly because of me) there's a way in Win7 to do reliable MUI cache invalidation. I haven't tested it in a while and assume this is the subject of a future post, so I won't reveal the secret.
Not that long ago I had to write code to enumerate user profiles in the registry, load the hive for that user, and clear the cached value (which is in different places on XP vs. Vista). We punted on the issue of roaming profiles. Look for the source in IECleanup.exe.