Recording is done by a background service: Windows Media Center Receiver Service. It has nothing to do with you desktop user login. Nor does it launch WMC. As for why it doesn't record, I have no idea. For me, WMC on Win8 is very unstable. It won't detect my HDHomeRun Prime tuners most of the time (a common problem). So, I won't trust any of my Win8 PCs to record TV shows.
You need to check your PC's event logs to see what error is WMC encountering while trying to record your show.