Changes in system time were traditionally another thing that caused issues, though that was most infamously linked to X inactivity timeout triggering screenlock, which wouldn't have been sleep(). It might have been nice to have had a SIGTIMEWHOOPS that gets sent on return-from-suspend, clock changes, and other real-world botherations of the normal happy computer model.

Another thought is that one could explore changing the sleep() model in the kernel; good userspace code should handle an early return, so coming back per the other interpretation might cause less trouble.