Currently we create a transaction with every object store in scope. This does not match spec behavior. Google says that they will align with spec too.
Didn't Microsoft say they currently align with the spec but think the spec behavior is dumb?
At this point it's clear that people agree that it should not create a transaction with all objectStores in scope. It's still discussed if it should throw or create a transaction with empty scope. I personally don't care either way.
This was fixed in bug 692669