When a friend a friend places them

When I place them:

My Modlist (Without Dependencies):
modlist.txt

Seconding this. It happens on a server here, too.
Only the player (A) placing the block sees it properly. Other player (B) can break the block. If Player B places the block again, it is only properly rendered for Player B.
After logging in and out again, both Players A & B see the block correctly.