max-build-height in the server.properties file doesn’t exactly correspond to the real height limit when playing. For example, setting it to 200 will allow players to build until the level 208. So 248 is sufficient to limit it to 256.
When higher than the render distance, one can see the sun below at midnight.
In SMP, hearts do not appear above Villagers when they are in “Love Mode” and try to repopulate a village.