The Stonestead doorpost can only be used to exit the building. (ie/translation: clicking the doorpost on the outside of the Stonestead building will not do anything.)
(don't know about this for other buildings, as no others buildings are available at this side)
(tl;dr version)

. . .
Depending on ones definition of consistency and its application, one could potentially argue its a somewhat inconsistent implementation.
(Don't tell me. It don't even matters at all in this particular case of course.)
--- --- ---
-- All buildings list --
Great Hall: Both ways. (checked against Valhalla hall, assuming its using same door-code)
Log Cabin: ...
Stone Mansion: Exit only. (Phaen post)
Stone Tower: ...
Stonestead: Exit only.
Timber House: Both ways.
Windmill: ...