Has anyone got any research on how this can affect users? I recently persuaded a developer to not use it. It was quite frustrating during testing to see the 'm

Has anyone got any research on how this can affect users? I recently persuaded a developer to not use it. It was quite frustrating during testing to see the 'mask' (made from underscores and slashes) expand and contract when they're typed over with non fixed-width characters of differing sizes. I'd much rather see three small input fields for a date (with some Javascript input filtering) than a field with some underscores and slashes inserted dynamically. I may be wrong.