I've noticed a number of times when closing my drivers door window that the glass reaches the top and then rather stopping starts to drop (happens via one touch, manual and with the key in the lock too).

 

Do I just need to give the top surface of a the glass a clean, or is there something more dubious happening?  I'm assuming the car is incorrectly assuming that something is trapped, and thus drops the window to prevent injury/damage.

It thinks something is trapped in the window. Clean the channels and then reprogram one touch.