Screen.sleepTimeout throuble

To prevent screen locking when playing with accelerometer I use SleepTimeout.NeverSleep. When player finishes level I set timeout to SleepTimeout.SystemSetting and show menu. But if timeout is small (10 - 30 sec) when level finished screen is locking (without dimming). It seems when Screen.sleepTimeout == SleepTimeout.NeverSleep screen timer is still counting. How to solve this problem?

Thanks in advance.