Interesting problem today.
Working on a clients’s 13 inch MacBook Pro that was having a problem where the machine would suddenly shutdown for no apparent reason.
After hardware tests revealed nothing amiss, further investigation appeared to indicate that the machine would shutdown at the moment the display was put to sleep.
Changing the sleep setting did not help. However…
Resetting PRAM (restart plus Command-Option-P-R at POST chime) and also resetting the SMC (see Apple Knowledge Base for your particular machine) seems to have solved the problem.
So;ution?: If experience unexpected power problems with your Mac, try retting the SMC and PRAM, then test to see if the problem is solved.
…Gunner