The reason is that LED brightness is changed via pulse-width modulation, IE they turn the LED on and off a hundred times a second or so. Whenever you turn electronics on and off, it creates an electromagnetic pulse. If not well shielded and filtered, it can cause interference with wireless devices.

Running the wires along the opposite side of the stem seems like a good thing to try.

One of the many reasons why I don't like wireless stuff. I don't see much point in it anyway, they seems mainly to be good for chewing up batteries several times as fast.