I've never used the original so this might be a faithful reproduction of the original (it's kind of cool), but it looks like the line tool and the multicoloured

I've never used the original so this might be a faithful reproduction of the original (it's kind of cool), but it looks like the line tool and the multicoloured tool interact weirdly, and it doesn't erase the previous line when you move the mouse, instead you get a cool fan of colour instead. I was expecting a single line, but had more fun with it as it is, which is why I suspect it might not actually be a bug after all.