[CQ-Contest] Is holding QRG's legal?

[Hal Kennedy]

Maybe I'm uninformed - but I figure this violates some rule in SS.
Heard yesterday afternoon on 20M:
 
Station A has a nice run going.
Station B calls in - an obvious buddy - maybe the same club?
Station A:  "Hey, hold the freq for me for a while, I wanna go check 15"
Station B:  "Sure."  Station B starts a run.
40 minutes later, Station A comes back on - "Okay, done on 15, Ill take
it back"
Station B:  "It's all yours, happy to help"
Station A:  Restarts his run on 20.
 
For those curious, I didn't quit for 40 minutes just to listen to this -
besides SO2R I have a third receiver here, which I parked on the freq to
see if the guy ever really came back - he did.  BTW, since I have the
QRG, calls and times, it is VERY EASY for the log checkers to verify
once they know to look....
 
Is this really okay?  If so, I need some helpers.
 
Hal
N4GG