That, and: I forgot to mention that not using the super builtin can also lead to unintentionally calling a method twice or more for the same base class in a diamond situation (note that with new-style classes, all multiple inheritance has at least one "diamond" class, often object, but people normally do not delegate to object for obvious reasons; you can imagine a base class Z in this example that A and B inherit from instead, if you wish). So, not using the super builtin can result in both delegating to a superclass' implementation too much, and not at all! This is a problem with multiple inheritance that Python actually solves; virtual inheritance doesn't touch it.
Note that `object` being the root of the class hierarchy implies that you must have careful coordination between all classes in a multiple inheritance hierarchy to determine, for a particular method, when subclasses may/must delegate to super, what the arguments to the method are, and even what the argument names are in some cases! You can't just go glomming classes together and expect it to go well unless you know the classes either don't use the same method names or agree very carefully on what the delgatable interfaces are.