When you attempt to place a block at Y=320 in Creative mode, the message "Height limit for building is 320 blocks" is repeated so many times you can't count them. It obscures half the world view and scrolls everything else off the top of the chat window.

Steps to reproduce:

1. Get into creative mode.
2. Build a stack of blocks up to 319, then try to add one more to the top.

Expected result:
The message "Height limit for building is 320 blocks" is displayed once, on the world view and in the chat window.

Observed result:
The "Height limit" message repeats, obscuring the view of the world and scrolling all other text out the top of the chat window.