Thanks for working on this! Remote Buddy is truly the killer app for the iPhone/Touch, in my opinion.

Here are the details you ask for (from my setup at least):

[a] no attached players (if by this you mean an MP3 player attached to the Mac when the problem occurs?)

[b] not playing off a shared library when I have this problem, but the library having this problem is able to be shared

[c] the local library is in the default location (/users/[me]/Music/iTunes), but my music folder is on an external volume

[d] QuickTime 7.4.1

I hope this helps!