@marcio After creating the fixture to test the touch screens I did notice that without the usb plugged in, when trying to calibrate the screen it will go grey for a second and quickly snap right to the main screen. My guess is it could be the marlin interrupting the screen calibration to display some error message.
This was caused when the usb board was not plugged in.
I can confirm that I am still seeing this issue on my printer running FW .78 when the usb is plugged into the printer
Quick edit: I can confirm that this is an issue with the usb take precedent over the functions of the lcd. If you begin the calibration with any usb, it will hang until you complete it. How ever you can force the calibration to end by inserting the usb.
@oliver: I see. What happens is that if the USB thumb-drive is plugged in, it jumps to the main screen to show that the drive was inserted, this will typically happen before the calibration screen has completed.
I don't see this as a huge problem, as users will not often have to run a calibration, but I could add an extra check to prevent this from happening.