And Schw

For me its not affecting gameplay as it dropped from about 200 to about 80 so still well above V-Synced 60 FPS.
Should I add a crashreport anyways?

I know that this was atleast intentionally introduced for stairs to prevent Items from getting stuck in them. (If the stairs were used to create floor patterns)

The problem is not the updating but the rendering of the item frames which has to be done apart from the rendering of the normal Blocks. There is not much wich can be done about that.

I've loaded such a wolr in Singleplayer and MCEdit and it wsa looking fine, but on a multiplayer server it happens. You can also get stuck in air or get set on fire, this is because the world is fine on the server but not for thze client.

I've also ran in this Problem and this is very bad, because it breaks most redstone circuits and maps.