I was really sure I had disabled Fast Startup in win 8.1. However, since that was your first concern, I double checked and I am embarrassed to say it is still enabled! :o I must somehow have forgotten to save the change. Changing that AND saving made all the difference. Now I can swap os ssd...
Same problem with two separate ssd
I have win 7 on a ssd in a PC full of disks.
I disconnected the win 7 ssd, and replaced it with a new clean ssd on which I installed win 8.1. It worked fine.
When I disconnect the win 8 ssd and connect the win 7 ssd, I get the following post when win 7 is...