In the documentation for auto_increment_offset the comment is confusing and is wrong:

"Should be smaller than auto_increment_increment, except when both variables are 1 (default setup)."

This is technically wrong. In a Master/Master set-up auto_increment_increment is typically set to 2 and auto_increment_offset is set to 1 and 2 (0 is not allowed according to the docu).

So correct would be: "Should be smaller or equal than auto_increment_increment, ...".

To make the docu more useful a good example would help. For example:

"Frequent seen settings for auto_increment_increment is 2 for both masters on a master/master set-up."

and

" Frequent seen settings for auto_increment_offset is 1 on one master and 2 on the other master on a master/master set-up"