Holding the window switches up forces the motors to stay on, trying to keep pushing up and the glass. This creates a heavy load on the electrical system because of the amp draw. Most power window motors have a "thermal protection device" that is basically a temperature-activated circuit breaker. When you hold the switches on like that, the heavy current heats up this device, and after a little while it kicks out. It's designed to protect the motor from overheating in the case of a stuck switch. When it kicks out, the motors are no longer drawing amps from the electrical system and the voltage goes up. It's not really a problem.
Weather stripping: I dunno. It would help to know which weather stripping you are looking to replace. Lots of different pieces of it around the doors, windows, rear slider, cargo lamp, etc.