And the right partition is exported, or nothing?
If it works, there's probably not much I can say, probably a weird quirk... I sometimes see a blank screen on *unplug* on FW 2.x (and then you just have to hit [HOME] anyway), but on *plug*, that's new

.
If it doesn't export anything over USBMS, then something indeed is wrong

.
(And, yeah, debug mode shouldn't impact anything regarding the usb mode screen).
In any case, I wouldn't mind taking a look at your syslogs (;dumpMessages).