Are both on at the same time? I have xlr connected to M11, and RCA going to Glenn 300B. I used to have the XLR going to V281, same thing. Strange.
Yep, both are on at the same time (at least right now ... I don't usually run it that way, just fired them both up together to test for you).
Only thing I can think of is that the Glenn 300B has something unusual with it's input impedance (since both XLR connections resulted in the same thing).