Petja:
all 8 wet/dry levels on that page change values between 0% and 81%
This is probably expected behavior – the levels settings are a "gang", where one can select 1,2,4 or 8 values. If you have 8 values selected when you assign the pedal, they will all change.
Your problems may be caused by your use of mono cables – you should try stereo ones (TRS – tip/ring/sleeve). This is because each socket is wired for a pedal, with the SLEEVE connected to one end of the pedal track, with the slider connected to TIP. If you use a mono cable, there will be no proper pedal voltage supply, just a high impedance feed connected to the TIP which is designed for switch operation, and will not do well with a pedal.
You may still have some underlying software issue (this is why we have beta releases) but the fact that yourself and your colleague have similar problems with both 5.3 and 5.5B suggest otherwise. If you have the patience, be so kind as to try TRS cables and let us know how you get on.
