Thanks for the reply, good to know! I was wondering if there could be a reason behind this behaviour, but if it's a known bug it's all right...
Sometimes when you have multiple points close to each other it's hard to shift-click each one, that's why I needed the marquee to work.
I've worked around it by adding middle points to the lines on less crowded areas and shifting them slightly so I was able to marquee-select the end points and move them where I wanted. Then I deleted the middle points.
Not super easy, but it worked for what I needed!