If you get to close to high power lines they may affect your craft, something similar to your situation happened to me, my P4 was about 30 feet away and 20 above a small 14,400 volt line and I was hovering, the bird all on it's own slide directly over the lines, and maintained altitude and stayed there, I had to move the stick a lot to get it moving.
The Electric field on AC power lines don't go very far, being AC the magnetic flux cancels itself, but high power lines are 3 phase and that generates a week field around all the lines. I checked out some graphs and they make some pretty cool shapes. My craft did not warn of a compass error, I think the field was not strong enough but enough to trick it in calculating that's were it was suppose to go. Others have had weird thing happen the their craft also, it probably depends on the load of the lines at the time. One thing for sure is that I'm not going to try to find out when and why with my bird, I will still fly above them but I will keep my distance.
