The attached screenshots show how the postern door is on high health (also seen by how it's not a pile of rubble), yet the actual door is missing. The screenshot also shows my character being able to walk straight through the door. It definitely seems like a bug to me and should be fixed because this can affect PvP greatly, as very little siege would be required to take the keep.
Also, I have never seen this before until this new patch came out today, I don't know if this is related or coincidental however.
UESP Staffer & Wiki Editor