There is a known issue (probably existing for quite a while) where the OS is too "extreme" in calling stuff unclean shutdowns. Currently if any process has to be killed in order to shutdown, then an unclean shutdown happens.
How it's supposed to work (and hopefully fixed next rev) is that only if the drives can't be unmounted cleanly even after killing a process if necessary should be "unclean"
At the end of the day, this means that most so-called unclean shutdowns (where a power failure isn't involved) aren't actually unclean. (90% of the time whenever this happens to me, I cancel the parity check after a couple of minutes, as I know that on the monthly correcting check it'll catch any issues)