How can I force Parallels to ask about re-associating my USB drive with my Mac or VM? When I plug in a USB drive while my VM is running, Parallels offers a dialog lightbox asking whether the USB drive should associate with the Mac or the VM. Once this choice is made, Parallels tends to remember/respect it on every subsequent reconnect. Sometimes I want to change this association, but I don't see how I can. Is there an easy option to change the USB drive's association on the fly? Or do I need to select something to make Parallels forget all USB associations and start over?
I had the same problem, with a USB disk drive. Parallels was configured to ask each time yet always put the device to the guest I'd first used it on. Choosing Parallels Preferences didn't help. The device wasn't listed as one that had a permanent assignment.

I think this is expected behavior as the documentation talks about a "New" device.

The fix for me was to Option-click (Alt-click) the Parallels icon in the Dock and choose Devices -> USB and there I saw the device listed with a tickmark next to it. Selecting the device removed the tickmark. Next time the devise was connected I was asked.