Turn-to-mute Bug

HTC devices with accelerometer such as Touch Diamond, Touch Pro and Touch HD has a cool function which is turn to mute. When a call comes in, simply flip the device face down and it will silent the call. This is another great innovation from HTC which was first introduced in the Touch Diamond.

On my Touch HD, it sometimes doesnt seem to work. By checking the registry, I found out that it has been disabled. It could probably due to certain softwares I installed which accidentally disables it. I then reenable the function and the problem occured again later.
After experimenting, I suspect it might not be due to the softwares I installed. Instead, it could be due to the ringing settings that I set.

Below are the scenarios I experimented:

1. Profile: Vibrate
   Turn to mute worked well
2. Profile: Normal, Ring Type: Ring
   Turn to mute worked well
3. Profile: Normal, Ring Type: Vibrate then Ring
   Turn to mute worked well
4. Profile: Normal, Ring Type: Vibrate and Ring
   Turn to mute was automatically set to disabled when a call comes in. Turn to mute function does not work for all future incoming calls.
   

I wonder whether it is my device only or is it a bug of the ROM. Well, at least this solved the mystery I had for weeks (or even months!). I think that the vibrate and ring mode is flawed as it does not have rythmic vibration pulses instead it behaves like the traditional windows mobile non-stop vibrating behaviour.