Logic Pro 9 Track allocations get stuck


I often find ( L9.1) that when I change the track instrument in Arrange, the allocation goes haywire.

eg. right now, I've switched a track to 'Kawai Piano' ( external instrument) in the track header, but the MIDI is being routed to an Instrument track 'MIDI Strings' ( K3)

yet another track, also 'Kawai Piano' plays a similar region back correctly.

When I select either piano track in Arrange, the same channel strip highlights in the Mixer, so there's no duplication.

When I copy the str-should-be-pno region to the healthy track, it plays as piano.

When I delete the copy, the original str-should-be-pno is now piano!

So something graunchy in there has been reset. A bit like 'rebuild mailbox' in Apple Mail :)

Is this a bug?