It's basically any option that calls Ctrl into play. It's annoying as hell ... please SE fix this. This was working perfectly fine until 2.1.
I, too, use legacy controls from XI and XIV 1.0 ... using numpad as my directional moving. Hitting Ctrl button while moving with the num pad will stop your character in place. (Hence .. any Hotbar key using Ctrl will also stop you in place from moving) This actually breaks my gameflow for advanced content quiet a bit.