Whenever I press "G" the selected vertices distort. The shape is retain with respect to the viewer but the vertices themselves are massively distorted. I'm assuming I've changed a setting without knowing. Can any help? This doesn't happen when I open a new file, but does happen in this .blend file everytime.
In the images below, I have selected the vertices I'd like to move, then moved them slightly. By rotating the camera you can see the actual damage caused.