It's also irrelevant to the underlying issue, which is how *nickel* itself is handling the unmount in order to export the partition over USBMS (which happens to be the *start* of the USBMS session, not the end).
The only difference the OS the device gets plugged into makes is in how it chooses to deal with the dirty bit being set.
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That doesn't invalidate what @davidfor just detailed about the recent (-ish) behavioral change re: how the import screen can be triggered and when an unplug becomes safe
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