I'm using a combination of PuTTY, tmux and vim. If I just open an SSH connection with PuTTY and then open vim, mouse scrolling works as expected. But if I open tmux and then open vim inside tmux the scrolling only partially works, meaning I can scroll downwards as usual but I'm unable to scroll upwards. If I scroll upwards the buffer just jerks "up and down" and just stays in the same spot. "set -g mode-mouse on" doesn't seem to make a difference (I do reload the conf afterwards with "tmux source-file ~/.tmux.conf"), works the same way either way.
Edit: I also noticed that scrolling works like expected in tmux in terminal but not in vim. Only options related to mouse/terminal I have in vim is "set mouse=a" and "set t_Co=256".