Sleep mode can't stopped before schedule ends

I have a sleep schedule from 1:00 to 7:00. One day I have an early flight to catch so I get up around 5:00. I manually exited the sleep mode from control menus. At first it seems to exited. But after some time, maybe 5-10 minutes, the watch went back to sleep mode again. I had to manually exit for second time, but it went back to sleep mode again! Again and again until I gave up and just waited for 7:00. 

Is this force going  back to sleep mode a designed behavior? Or it's just a bug?