Whatever it was, it was obviously something Emu had to fix. I'm with Mac in that it likely had to do with the multiple port selection scheme in RB. Heavily registry reliant.. looks for what the OS reports back as a good driver.
They probably focused on the 'plug-n-play' aspect where it loaded itself up and took over without properly registering, if I were to take a guess. Jeff Y is probably one of the few that know the underlying issues.
Just glad it got fixed, as I know we have one of these in the studio, just haven't had cause to use it lately. All the systems now have regular MIDI connections. But someday we may want to use separate ports again..