I've never had this problem, but I'm betting the button is getting pressed by accident by the cat or your kids or something. Try this: when you pause, don't leave the cursor on the 'resume' button, where it defaults to. Select the quick options menu, then select something (unimportant) in there so that it would take a few button presses to go back into the race. And hide your controller lol.
Indeed, and it's kinda why Endurances races are pointless and very boring in GT games. In the real world you have so many things to worry about whilst driving, knowing a crash could put you in the garage for three hours, or a puncture could set you back considerably amongst others. In GT5 with no damage and no mechanical failures it is just driving for 24 hours, there is none of the challenge and excitement that a real endurance race brings.
Don't people have jobs in Newcastle?Saving during an endurance race defeats the point.
Not having a game save for a 24 hour race is just brain-dead...especially in this era of energy conservation.