Timers that are counting down in the game aren't counting down to zero correctly. When the timer reaches 00:01:00 it immediately resets to zero, instead of counting the last second as well. GLaDOS is also saying the numbers at the wrong moment, for example, she says two when the timer says 00:02:59, when she should have said it when the timer read 00:02:00. (However, these errors were corrected when the game was released for Mac OS X.)
When Valve attempted to solve the error of Chell being able to fall from incredible heights, it added the plug leading from the back of her foot to the back of her knee to strengthen her muscles. However, without any back support including an exoskeleton or bars stronger than human bones, there is no way she can be completely protected.