I discovered today that you cannot use setblock command any more to place a sign at the position of another sign. The game just says "the block couldn't be placed". This did not happen in 1.11. The game seems to have no problems placing a sign in the positon of any other block unless it is already occupied by another sign.

To replicate:
1. Give yourself a command block
2. Paste in this command "/setblock ~ ~1 ~ standing_sign 0 replace"
3. run it
4. run it again

It will fail the second time and say the block couldn't be placed. This may seem like a trivial issue but no matter what the sign says or what commands or syntax is imbedded the result is the same. As a result of this bug I can no longer update signs that the player interacts with remotely such as changing the text or the item they are purchasing. I would instead need to remove the sign entirely, then put the new sign there which is twice as many steps.

If this is the same for all tileentity blocks (I haven't checked) then it would also make replacing the contents of chests difficult with setblock. Setblock is far more convenient then replaceitem as you don't have to place in items one by one and can update the interface in one command.