Weird! It sounds like you've got a short somewhere that's going to ground right there. Is there a wet or damp spot in that door? They might be getting shocked through their feet. Try to look at all the electrical wires run on that side of the building. Maybe a mouse or something gnawed into them. Be careful, but try putting the back of your hand on the ground and on the building in various places to see if you get a tingle but you may not if you've got shoes on. Years ago my parents had a travel trailer hooked up via an extension cord out in the yard and every time I'd step down off the step and onto the ground while holding onto the door, it would absolutely unwind my clock. I told them but no one would believe me because it didn't happen to them. The difference was that I was BAREFOOT and they were not. Sounds like something similar happening to your horses.
looks like we are thinking the same lines.........animals sense stuff like that way b4 us.
I still can't figure out if the two events are related or just coincidence. We did feel around just like that because my electric fence is the same way, touch it with thick rubber shoes on and it's like the fence isn't working... touch the ground with your other hand and it zaps.
That same thing happened to me with our RV:).
I hate being shocked, even a small one. I get very unchristian when it happens:)
Becky