[Matthew Steel]

ProTools does not support arbitrary MIDI control of parameters. It only supports its own (undocumented) control surface protocols, and two documented legacy control protocols. The documented protocols are for the JL-Cooper CS-10 and the Mackie HUI. This limitation is on purpose so that Digidesign can sell control surfaces. So perhaps it is not a "flaw" but certainly is a major LIMITATION in ProTools. But it is on purpose so Digidesign can sell control surfaces.

Do some searching and reading on the CS-10 protocol. It may do what you want. IIRC it uses a predefined mapping between CC numbers and faders. It does not support motorized faders so if a fader changes from ProTools then you will have to move the fader through the current point before ProTools will respond again. In your case your keyboard isn't likely to have motorized faders so this is probably the desired behavior.

The Mackie HUI has the limitation that there are periodic status checks. ProTools will periodically send a message to the HUI and expect the proper reply. If it does not get the proper response back then ProTools assumes the HUI has gone away and disables it. So to use the HUI protocol you need to be able to program your keyboard to spit back the response every time it receives the keepalive message from ProTools.