If you want to verify this for yourself, just try it out on your favourite ladder. You will see that the top pulls away from the wall just before the ladder becomes horizontal.

To understand mathematically (or rather, physically) why this is true, suppose for a moment that there was no gravity. Then, when you pull the ladder, you will pull the entire ladder as a unit, with both top and bottom moving away from the wall with the same speed.

A good exercise is to try to figure out the equation for the position of
the top of the ladder during this free-fall stage.