Revision history [back]

According to the documentation on class functions,

NOTE: The ordering of the columns of the character table of a group corresponds to the ordering of the list. However, in general there is no way to canonically list (or index) the conjugacy classes of a group. Therefore the ordering of the columns of the character table of a group is somewhat random.

I've used this functionality a fair amount but to my surprise there doesn't seem to be good direct documentation of character_table easily discoverable online. You have to know that it lives here, and it doesn't say much more about it than to ask how GAP orders it.