Last week I encountered this issue. I add a cube via append in the subtool palette. When I try to move it, it begins to stretch. Even turning off the symmetry doesn’t help. Unfortunately I don’t have the file right now but I recorded myself facing this issue.
It has happened with my multiple times but very less often. I don’t know what exactly triggers this. It seems as if I press some key that toggles this mode on.
It does not happen when I start a new document from scratch.