"Short" is a commonly used term to describe almost every electrical problem, mostly by people who are unfamiliar with electrical wiring and troubleshooting. Shorts cause arcs, sparks, and trip fuses and breakers. Opens" created a difference of potential that causes current to flow when something like a hand or body is placed across it such as standing in water and touching an ungrounded frame.
We have to assume the OP's trailer is correctly wired because he did not indicate a problem when hooked up at a campground. So, the trailer and shore power cord can be eliminated. The problem is an open ground somewhere. If the problem occurs when he plugs into his garage outlet, that leaves two possibilities. One is a misfired outlet or if it's an older structure, it was common practice to not use safety grounds at all. Fortunately, current electrical codes have fixed eliminated that practice. If the outlet checks out OK, then the next likely cause would be any adapter that is used to between the trailer and the outlet. Those have been known to fail and create shock hazards. It's also possible that if the trailer is at fault, the OP may or may not have experienced it at a campground unless conditions were just right, and if everything else checks OK, the it's possible that ground and neutral may be tied together somewhere in the trailer or a ground wire has come loose at the power distribution panel. At any rate, a ground has been lost somewhere.
I recommend that anyone not familiar with electricity get a qualified person to check all of this stuff out. Electricity is serious stuff and not for amateurs. The lives of you and your family are at stake.
2013 F250 XLT
I now have a Keystone Outback, but I try to help when I can.
Bitter Gun Owner