Well I thought the problem was solved, but just discovered another glitch. Everything works fine EXCEPT when I leave my HTC one connected via usb and the Hot Sync Manager open. Then the screen freezes when trying to come out of sleep, but I can unfreeze it by unplugging the HTC one from the USB cable (leaving Hot Sync Mgr open), and then sleep mode works fine and system restarts without problem. Likewise, when I leave the phone connected via USB but Hot Sync Mgr not open, sleep mode works fine.
In other words, Sleep Mode works fine except when the phone is connected via USB AND Hot Sync Mgr is open.
This is not a major issue for me, as I almost never leave the phone connected via USB, (which is why it took so long to uncover the problem). But if you have any suggestions I welcome them.
Thanks