Though, I'm not really sure why LibJostle is trying to move the frame in combat anyway.
Because it tries to do stuff on entering and leaving combat and whenever certain events fire. Checking if a frame is secure would be silly in combat because the entire default UI starts as secure, checking if a frame is protected though could be a possible addition. Also LibJostle is a relic of the WoW 1.x days which is why it doesn't do any of that.
And yes I am technically the current maintainer of LibJostle-3.0 and no I have no plans to rewrite it or anything. If people submit patches then bring them to my attention on IRC, I will look into them when I get a chance.