Connected to my box via Putty.exe
$ tmux list-clients
/dev/pts/2: 1 [80x24 xterm-256color] (utf8)
/dev/pts/9: 1 [94x30 linux] (utf8)
$ tmux detach-client -t /dev/pts/2
the terminal flashes resizing the window to the full 94x30 for a moment and then immediately resizes it back to 80x24
$ tmux list-clients
/dev/pts/2: 1 [80x24 xterm-256color] (utf8)
/dev/pts/9: 1 [94x30 linux] (utf8)