They will blame both initially. Pissed off people are pissed off, and distribute blame randomly. That is the short term pain. However if it broke AND Microsoft stated up front that it really was Adobe's fault, Microsoft would have taken less of the blame. Not none, but less.
The flip side if Microsoft had bitten that painful bullet up front, then I believe that going forward companies like Adobe would have learned to not try to hack the system like they had. That would have given everyone, including Microsoft, a better reputation.
But of course Microsoft did not do that. And now Microsoft has such a history of nasty bugs that, even if Microsoft is in the right, nobody is going to believe it. (Which of course locks Microsoft into its current strategy of bending over backwards to accommodate everyone else's bugs, causing more bugs...)
