The silent call problem has happen to me on a HTC Desire (in Australia) and had to reboot,
but I did notice the the headphone icon was on before the reboot.
After reboot no headphone icon and all ok.
Am running the beta Audible for Android app and I was listening with headphones earlier in the day.
I know the app is in beta and main problem for me is headphone controls do work.
I may not have been the Audible app, will keep an eye on the headphone icon from now on.