Incorrect bulb operation is usually due to a broken ground circuit. Current goes through the brake bulb, but cannot get to ground for the return path. It finds an alternate path doubling back through the tail light bulb, over to the other side, then through that tail light bulb, then to ground. To verify this, observe how the left-side bulbs work, then see what happens after you unplug the right lamp assembly.
Wednesday, September 20th, 2017 AT 6:47 PM