Windows shuts down when should restart

I support an automation lab. Sometimes systems seem to shut down when they
are supposed to restart. I have never caught a system in the act, but I see
it in the automation logs.

The most common time for this to happen is switching between OSes. Each
system has 4 OSes (xp,vista, 32,64, mix 'n match). The system uses batch
files to set up a change in OS. The shutdown command used in the batch file
is

shutdown -r -f

Are there known cases where a XP or vista machine shuts down instead of
rebooting? Googling this sort of thing gets me huge numbers of useless (for
my current problem) "my windows won't shut down" pages.