You should be able to get the car dock detected if the dock is Unplugged, not sure why. But I have noticed that nothing will get the home screens into landscape mode. I used to skip the car screen, but really liked the home screen, dialer and phone screens to be in landscape mode.
I have a workaround, I installed Go Launcher, and an app that launches it when the phone is plugged in. This way when I insert the phone into the dock, Go Launcher launches. Also, I set the phone button on Go Launcher to use Go Dialer, this puts the dialer in landscape also.
I guess any alternative launcher would work if you don't like Go Launcher. I forget the name of the app that automatically launches something when the phone is plugged in. I'll post it later when I look through my app drawer and find it.
I'm hoping that HTC notices that GB killed the car dock and fixes it with an update, but I'm not holding my breath for an update. I still like my tbolt but I'm beginning to think that us tbolt owners are one big soak test.