Why do I get "no volume available" when using an iPhone 4s in a dock?

I am suspecting it may be the "Griffin TuneFlex 9865" that I am docking the phone with. Yet the the dock is designed to just provide charging power and to hold the device, there is no line out on the dock. That I could see. But every time I plug in the iPhone into the dock to charge, and then plug in the head phone jack going to a line in on the car, there is no sound.

When opening the Pandora app after doing the above it shows "no volume available" where the volume slider should be. If your in the "Music" app the volume slider is gone.

Any idea why this is happening? Does my iPhone think the dock is a line out source?

My workaround has been to unplug and then replug the headphone jack, and then all is well and it works fine, until I remove the iPhone from the car, then repeat.

Is there a way to make it work right the first time I plug in the mini jack on the iPhone and have sound?

Yet the the dock is designed to just provide charging power and to hold the device, there is no line out on the dock.

This is incorrect. The description for this device on Amazon (sorry, I couldn't find any information on it that wasn't on a for-sale site) has this feature listed:

• Built-in, 0.125-inch stereo line-out audio jack lets you attach an audio cable directly to your stereo, or run the included cassette adapter into your stereo's tape cassette player

Apparently the device does have an line out on it some place. And this is why your headphone and volume controls are disabled when you dock your phone in it.