Hello,
I have posted the 8.1 Release Candidate which addresses the crashes:
Download 8.1_M0_Release_Candidate_8.1.855_Installer.zip
The shutdown being longer has been accepted by Microsoft as a bug: we fixed a bug in our code which made an OS bug visible.
There was not enough time to safely revert our fix for 8.1 M0, so we will reintroduce our bug (!) for 8.1 M1. Windows bug will be fixed in next OS version.
Kind regards,
Alban