Grohtherm 1000 - 34154 Shower - Hot and cold opposite

Just had one of these exposed units installed and hot and cold water comes out the wrong way around. When you select hot you get cold and when you select cold you get hot. Plumber has checked and hot pipe is connected correctly to left side. He says that there is nothing that he can do.
Any ideas?

Thanks.

ARH.

Hi

Contacted Grohe and they confirmed that this was a factory fault. They came out and swapped both units out under warranty.