Hi,
I've just tested this, and then tested it again because I couldn't quite believe it...
It seems that the curves editor behaves like this only when it is plugged into the 3ds Max composite map. It doesn't appear to happen with other maps.
Windows scaling was my first suspicion but it doesn't seem to have any effect.
I'll send this onto the devs so we can figure out what is going on.
Thanks,
Rowan