What happens if you only select foot & defrost? Do both blow warmed air? How about if you select AUTO air distribution? Perhaps the fix is to use another setting or a slight adjustment of how you already have things set (temp & auto vs manual air distribution/air duct direction/etc).
There's a small fan inside the IHKA control panel that sucks air through the grid on the left side of the IHKA...this function draws air across a thermistor which helps the IHKA regulate and maintain the temperature you have set on the display.
Make sure that the air vent above the IHKA isn't blowing downward toward the IHKA...if so, it can cause that sensor to cause the IHKA to regulate incorrectly. The issue is usually the opposite...there's a TIS for complaint of hot feet...due to cooler air from the center dash vent being pulled in across the thermistor...which causes the IHKA to send hot air to the foot wells: