Sorry for letting this slide for a while...

Can you check (in Programs and Features, View Installed Updates) whether you have KB2999226 installed? If not, you can get it from https://support.microsoft.com/en-us/kb/2999226

In the first install, this component failed (hence the missing DLL error), and then in subsequent installs it wasn't re-run. I'm not sure exactly what happened here, but it's possible that the installation was deferred until the next reboot automatically. Being a Windows Update, we don't have much control over how these are managed and the operating system can basically do what it likes.