Thanks for the confirmation. BTW, I've just found
Shut It! that may be the tool you need to prevent the PC from shutting down or going into sleep mode, while still permitting it (or even forcing it) when the encoding and muxing processes are finished. I haven't tried it, and I'm not sure it will work, but you may want to have a look.
[EDIT] Sorry, but it seems that it is no longer possible to download it. If you find a copy somewhere, please let me know...