Maybe this is the same issue we are having with serial from MSC and Denon DVD's in general.
I had it with old DVD's (1940CI) and with Blu-Ray's (2500BTCI) and now I hear there are issues with new 2010CI's. After this ordeal I have switched for a while to other brands until this is rectified.
The issue is that they just don't seem to work with MSC the same way. Every unit or unit - MSC combo needs to be set to something else. Try experimenting with parity (none or even) and CR enabled or not. You have to find right combination. I know how it sounds. Ridiculous. But the truth is I have installed many, many serial controlled units and all seem to have one common characteristic: They work exactly the same way. Once protocol, port settings and cable is figured out, it always work the same way. Not with Denon DVD's.
AVR's on the other hand are rock solid - never even single issue. Weird.
Remember that if you record macro directly from "connected devices" all RS232 commands come in checked to repeat. I'm trying to make URC fix it but since it is not a critical issue (you uncheck it manually and it is fixed) it probably will be fixed - to use RTI's mantra - in two weeks.
Piece.