R5291 - changing clef doesn't change notes in the part

Just been doing some guitar parts in R5291.

This emerged after an import from PowerTab via MIDI File Import.

MuseScore imported the file in standard treble clef, which meant all notes were displayed in ledger lines :)

On changing the clef to the guitar standard Treble 8va the notes remained exactly where they were.

On experimentation I have found that changing the clef has absolutely no effect on the notes in that part.

Is this a known bug?

Or should I file an issue??

Oh OS is Windows XP Pro SP3