Comment 13 for bug 14620

One other possibility comes to mind: just before any resize operation, partman
commits any previous partitioning changes to disk. This could certainly involve
partitions being created or removed, which would trigger hotplug events.
Furthermore, sometimes there's an asynchronous delay between hotplug events
being generated and udev getting round to processing the events as device node
changes. So, even though partman runs ntfsresize synchronously, it's possible
that hotplug events left over from the previous commit operation could intervene.

The simplest solution would probably be to call udevstart somewhere in partman's
commit.d scripts.