[briggs]

I found some reg keys that I think are causing the ringtone to revert in Mighty 4.2;

HKCU\ControlPanel
:Ringtones=\Ring-WindowsMobile.wma
(data never changes no matter what you set the ringtone to)
I don't know if this one causes a problem, I'm not going to delete it in case it is the key that is actually causing the revert, but I'm guessing it's the stuff below that was causing it.

HKCU\ControlPanel\Sounds\RingTone0
:SavedSound=\Windows\Ring-WindowsMobile .wma (never changes no matter what you set the ringtone to)
I think that we need to delete this reg value, I have.
:Sound="the file you set it to (until it reverts then it's the above)" - don't delete

HKCU\ControlPanel\Sounds\RingTone2
:Sound="the file you set the ringtone to even after the RingTone0 reverts"
You can probably delete this whole reg folder now after the savedsound value is gone from Ringtone0.

I'm guessing this was the problem. Test this out over the weekend and tell me if the reversion happens. Hopefully, we'll get this fixed for Mighty 4.3.