fscking any mounted filesystem, even if it's read-only, on any Unix that I'm aware of, can have such problems. The problem is that the OS expects that it's the only thing modifying the filesystem. When you run fsck on the device, it ends up modifying the filesystem. The OS has absolutely no way to know this. So it's easily possible for it to encounter inconsistencies and screw up in undefined ways.
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Bitt Faulk