Before I start let me explain that prior to upgrading to Win 10 my Win 7 password was not the same as the one for my Microsoft account.
With a lot of trepidation I decided to upgrade from W7 to W10 and it went completely seamlessly, well done Microsoft. Next day when trying to start up again Windows 10 would not accept my password which I was 100% confident I had entered correctly. After much head scratching I decided to try my Microsoft account password and Win 10 accepted that and started so it seems that the upgrade changed my Windows logon password to the same one as my Microsoft account. Is this expected behaviour?
For the avoidance of all doubt never at any stage did I update my user profile within Win 10 and change the password there.