Oxygenics showerhead

Have an Oxygenics showerhead with the push button shutoff valve. The valve doesn't actually shut off the water but reduces the flow to a trickle (by design). When we "close" the push button valve while lathering up, the temperature of the trickling water goes from the set temp to straight cold water. When you turn the valve back on, cold water flows for a few seconds and then the temp returns to the warm setting. Anyone else have this problem. How to solve?