This is just a quick heads up to keep a look out, as well as another reason to install Windows 10 fresh. Upgraded my licensed copy of Windows 7 HP 64 in a VM to Windows 10 Home 64 a while back. Yesterday I encountered the 1st serious problem. Running the Adobe Flash full setup [rather than web installer] for the new version out this week I encounter Direct X 9 errors. It didn't used to, & it may have as much to do with Flash as with Windows, but the show stopper for me was when I compared Direct X on that win10 VM with my separate win10 VM -- it's an Insider Preview that was installed fresh rather than upgraded from 7/8.
I also checked my regular versions of 10 [64 & 32 bit], but was more interested in the VM because the VirtualBox Additions have to do with DX too, & so the DX-related files in Windows\System32 are a slight bit different.
At any rate, the upgraded 10 had a much different Direct X install. And it is not compatible with or interchangeable with the normal Direct X for 10. I've been a bit gunshy when it comes to Direct X installations since XP -- when/if they go wrong, very often the only fix is a Windows reinstall -- so it was enough for me to make the decision that next ISO release, that win10 VM gets a fresh install. I don't want to wait & see if further problems develop in the future, when there are more win10 updates etc. to add to a fresh install, but would rather get the foundation right from the start.