Steven's hair length fluctuates between shots.
In one of the first exterior shots of Steven's new high-rise apartment, just before Roger breaks in, Francis and Merton can be seen on the ledge, obviously taken from the later ledge scene.
When Wilbanks and others are watching Steven's apartment, they are using an astronomical telescope and looking directly into the eyepiece. Without an erecting prism the image should be upside down, but the view that is seen is a normal image.
When Wilbanks and Mertons are on the ledge high up outside the building, at one point Mertons falls over backwards and hangs upside down, but his hat, which is shown to fit loosely on his head, does not fall off.