Transmission zeros created when selecting outputs in state-space system

I have a MIMO state-space system with inputs of rotor speed (quad-rotor plant) and outputs of the states (U, V, W, Phi, Theta, P, Q, R). This system does not have any transmission zeros. As I create a smaller plant with the same inputs and a reduced output set (W, Phi, Theta, R), two transmission zeros are created. I arrive at the same result when using balred() and minreal() to reduce the plant order.

Is it possible for a plant to create these transmission zeros or is this an artifact of how MATLAB reduces the plant model? Can I trust that these transmission zeros are real?

Thank you for your time, Clay

[Martin Evans]

I have exactly the same issue and I haven't been able to work it out. I can only guess it's an artifact unintentionally added in the balred function.