Well I just bought a used TU2 for 40 euros and when I got it I cleaned the pedal with alcohol to get rid of all the dust. Put it on the pedalboard and stayed there for a few days.
Today, and to my surprise the plastic cover that protects the leds and the LCD display had areas that the black had come off and instead there were white fog ares (hard to explain).
It seems that the alcohol got underneath the plastic and reacted with the black paint on the cover...
The pedal works fine and luckly the reading is the same, it's just damn ugly to see black and white areas on the display.