I agree, it is very annoying. I don't know why it keeps activating but when I go into the UV editor to move uvs, it just slides. I have to keep going to the move options to turn off transform constraints while wondering what turned it on. It's very annoying and would like to permanently disabled it. I haven't needed that feature since starting to use Maya version 3 and doubt I would ever need it. If there is a way to permanently disable it off on Maya 2018, please inform us. Thanks