The original iron door texture was mostly a regular (now oak) door, edited to have a color change and, more importantly, missing its handle to signify it could not be opened by hand.

This intentional detail, which helped new players understand its function, was seemingly unintentionally missed when updating the iron door texture during the texture update.

Asides from possibly aesthetics, there's nothing that points to this being working as intended.

Door renders taken from the Minecraft wiki.