Altium - Strange issue with Library part
There is a little purple snot at the left hand end of the mechanical region (Just about visible on the screen)....

Mechanical outlines are rectangular bounding boxes so the presence of that little bit of line causes the size of the bounding box to do what you are seeing. 

Remove it, save, do an update from libs and things should become more sensible.

This one gets particularly annoying when the object causing the problem is invisible, you end up using the pcb lib inspector and list to track it down and kill it. 

I am guessing you have the option for what to put under the mouse set to component centre rather then pin 1, which makes this kind of thing even more aggravating.