The in-game chat(on-screen not the chat log) stops displaying after the client transitions to a new map after downloading it. The chat started displaying again after a few minutes. I think this issue may be caused by the amount of spam caused by the downloading text. It was displaying text for every 2 KB of the map I had downloaded, so it was flooding my entire chat log with text.
Steps to repro:
1) Join a server
2) Allow the server to transition to a map you do not currently have, forcing a download.
3) Note the serious "Downloaded xxxKB" message spam.
4) Notice when you load in to the next map that your chat no longer displays anything.
This occured 1/1 times for me, I may delete some custom maps to test this again. I will update this thread with more info when I get it.
