W35i screen randomly turning upside down

Hi, we're using more than 50 mini2440 boards with W35i LCDs and sometimes
(about once per week) the screen get randomly turned upside down (just the
image, touchscreen works normally) and stays so until reboot. LCD is
mounted in custom made metal case. We found out that shock from static
electricity causes it (when somebody not wearing antistatic wearing touches
it, it happens - again, only sometimes), so we power grounded the case and
isolated it from display circuit, but the issue still remains. Does anybody
encounter similar problem? Any ideas how to solve this? Thanks in advance

Some displays support two digital inputs to define the scan direction.
Maybe one of these lines are floating and the display interprets it mostly
correct, but sometime incorrect. Take a look into the data sheet of the
used LCD and measure the voltage level at these lines at your display unit.

Also consider grounding the touch screen outer surface with a conductive
material in your mounting. It will have to be a soft material that does not
put pressure on the touch pad.