Drive letter goes missing on XP SP2

My file system mounts UDF on CD/DVD media. During testing on Windows XP SP2
I noticed that sometimes (90% of the time) Explorer will remove the drive
letter which is mounted by my volume. The drive letter is still accessable
to the user in other applications; but not in Explorer. I must close and
restart Explorer to get the drive letter to show up again.

MORE INFO: My drive letter goes missing after a call to the Win32 function
SetVolumeLabel(). The function is successful and my file system changes the
label on the media and further returns success to the caller.

Very strange. Does anyone have any ideas what might be causing Explorer to
remove my drive letter from its drive list? I assume it’s probably some
state of the CD/DVD drive…hmmmm?