Weird system issue

While I was listening to an album last night, I turned on the CD player/recorder to sort of A/B the sound between CD and vinyl.
As soon as I powered on the CD deck, the output from the turntable muted. The source selector was still on phono but there was no sound output.
As soon as I switched the source to CD and pressed play, the CD played. As soon as I pressed stop and shut off the CD deck, the sound from the turntable gradually ramped back up. Any suggestions, ideas?
I recently purchased a used Rogue Magnum 66 pre amp to go with my Anthem power amp, Scout turntable, Denon CD player/recorder and Vandy 2C sigs.
The CD player recorder is connected in the tape loop of the pre amp, using the CD as the input one of the pre outs as the output. But even when I switched the source to tape, there was still no sound from the turntable.
Sounds like it the tape loop. Did you try switching the source to Phono on the record side of the loop? I am not familiar with your pre amp but that is what I think of first when reading your chain of events
I will recheck the cabling tonight. I guess that could be it but would it mute the phono just turning on the CD recorder, with no signal coming out of the CD?