Steve asked me about this when we were on grid and I couldn't think of anything that would cause that. At first I thought he might have been hitting readline since no one actually looks at the tacho during a run (do they?). But on the way home I remembered reading about something like this on cobb's forum:
http://www.wrxforum.com/cgi-bin/ulti...c;f=8;t=000149
I think I might have read of this somewhere else too ... the only other places I go to are nasioc and i-club so maybe try searches there.