Do you mean you highlight something in the Mask and then it isn't replaced? In that case I observed that and it's tracked here: https://www.ventismedia.com/mantis/view.php?id=18321

When editing values in the auto..* dialogs patterns,
like: "Auto-tag from filename", "Auto-organize files",
selected/marked values are not replaced, when choosing a different value per ">>",
but added instead.
Thats a bit inconvenient, so probably not meant to be that way?