Hi,
My RC-50 works fine, it could be a configuration problem. Have you checked the Tempo Func option (CTL/EXP button)? Does it say "SYS(tem)"? Have you tried "PAT(ch)"? See page 70 of the manual.
Regards,
Sjaak
Regarding the RC-50 -- I've observed this when I record a loop then change the tempo. It follows that a track, recorded at one tempo, then played back at another would do the same thing.
-- Kevin