Aaargh!! Finishing my second paragraph ...
in reply to a message by Elinor
"But I doubt their parents have met many - if any - male Killian's, and thefore they are going by sound alone because they have no connotations to go on. With John, the name is set in their mind as referring to a man, and being so common, it seems to refer almost generically to any man, making it very weird on a girl."