Deliberate mistake: When Tarzan fights with the leopard, it scratches his chest. However after they fall into the pit and Tarzan comes out carrying the dead leopard, the scratches on his chest have amazingly healed. [It is a long-standing Disney tradition that no evidence of violence is shown on screen. Still a mistake, but there's why].
Deliberate mistake: When the characters are crossing the street to get to the toy store, Mr. Potato Head gets his foot stuck on some gum. From the first angle, the gum is at the half way point of the rolling cement drainage pipe. When he barely escapes, the gum is near the lip of the pipe, a foot or so from the end. As the gum sticks to the passing pipe, it appears to be half way between those two points. (00:38:15)