Thank you for telling me!
About Liv, the actual pool of unlockable characters only updates at set points in the story, not whenever you defeat an enemy. You'll need to defeat the tunnel boss to get access to more revivable characters ^^
The middle click happening on its own is very strange though, I've never had any reports of this, and it never happened to me... Even if it was on a different computer, did you use the same mouse or keyboard on these two computers maybe?