Yes.

Check to see if the compressor switches off when the heat comes on. If it does, you can probably forget about the monovalve repair kit. A poor electrical connection at the monovalve can cause the heat to come on when it is not selected, but that won't cause the center vent configuration to change. It could be working backwards due to a simple vacuum plumbing error, but it's not going to change unless the CCU "thinks" it has changed modes.