Why does this receptacle have the ground tied to the neutral?
Yikes, good find! This is most definitely the reason.  The ground and neutral are only supposed to be tied together at the main panel.  In this case, instead of only the neutral carrying current, both the ground and neutral will carry it.

There is no legit reason that I know of to do this at an outlet.  I wonder if perhaps the neutral was open and the previous person was trying to cheat to make the outlet work?  Do disconnect this. I would check other outlets in the house. An outlet tester may help speed this up but they don't detect all conditions.

Grounding is an important safety aspect of your house. If you suspect there is a more systemic problem with the houses grounding, get an electrician to take a look. Better safe than sorry.