Why is Water only flowing through flow side of t bar mixer

Fitted a shower thermostatic t bar mixer and water is not flowing via thermostat side. Due to the pipes being opposite of how they should be, hot is right, cold is left . So Thermostat is on the left. Flow is on right. When correct fitted (shower hose outlet down) I get only cold. With hose outlet facing up, I get only hot. I turned of cold water supply with hose outlet down. I should get hot water but no water comes out. Turn back on cold supply,, water flows. Turn t bar with hose outlet up, turn off hot supply should get only cold water but nothing comes out. Turn back on hot supply, hot water flows. Have I missed something ? Henderson