Hunter Ceiling Fan 25885 remote won't turn off light

When I flip the wall switch, the light comes on as expected. I can press any of the fan-related buttons on the remote and they work fine. The light button does nothing - the light stays on. Only two wires come into the unit (black and white) and the light kit is properly connected to the dangling connector, so this is not a wall-switch problem. I tried to get a manual from Hunter but the unit is too old. I looked online for a wiring diagram, but again could only find diagrams for more recent units with different wiring. The Receiver model is CP-9110R. Most of the wiring is as expected (pink to pink, gray to gray, yellow to yellow, B/W to B/W, black to black). The one oddball thing was there is a red wire coming from the fan assembly that is twisted in with all the white wires. Anyone know what that red wire is for? Anyone have a wiring diagram or instruction manual for this fan or receiver since Hunter isn't helping me (twice they said they would TRY to find a physical manual and get back to me). If the wiring is correct, then I may need to replace the receiver. It worked this way when I moved in, so I have no way of knowing if it ever worked correctly with the current wiring configuration.