NetPerfMonService.exe takes 10-15 minutes to stop

During any upgrade of APM (SP1, SP2) when the NetPerfMonService.exe is stopped it takes 10-15 min.

I see the memory slowly counting down, first in 22k blocks, then 44k, then it eventually goes down 140k or so at a time until around 230K or so and the service finally stops.

 Any ideas?