Well that's interesting. There are two nearly identical keyboard mishaps that can wedge a screened process, and they both require ^Q to recover.

I've always attributed these hangs to the sad fact that hitting ^A can fairly easily come off as "^A ^S", especially when you do the keyboard hit with a slightly rolling hand motion. And as that key combination means "send ^S to the process inside screen", it results the inner process receiving SIGSTOP. Of course, the recovery is nearly the same as in the article: ^A ^Q.

For a screen user both have the same cargo-cult solution - just send enough SIGCONTs to the screen to get the application responding again.

I suspect that tmux chose ^B as the default command key to prevent accidental process hangs.