Lighting problems. Ballasts wired to other fixtures.

I work in commercial maintenance. I have 3-lamp parabolic light fixtures in my office buildings. I have a fixture with two ballasts, one 2-lamp 120/277v the other a 1-lamp 120/277v. When disconnecting power to my 2-lamp ballast I lose power to 4 other light fixtures in immediate proximity. How is it possible that this happened?

I'm thinking my fixtures are somehow tied into eachother off of one run of MC at a j-box.

I don't think rewiring all of the fixures with a 3-lamp ballast is the solution without running more MC to each fixture, tying them together on the circuit.

Help?