I think men, especially men such as Tolkien, often have this sense that women are changlings who never seem the same they once or first were or who constantly confound them. And having had that experience, they don't much like to tell of of it, unless it can be put down to the woman's questionable slipperiness. It wouldn't bear telling about much, so it isn't something Tolkien choose to elaborate upon.
Or something like that.
