I dont' know if this helps or not or if I just dont really understand the problem... but when one of my brake lights was out I purchased the wrong bulbs, it only had a single filament and the same thing was happening to me.. the 3rd brake light was always on and my brake light wouldn't really get any brighter when I hit the brakes..

The real bulbs are dual filament, the second filament is a lot brighter than the first which is when the brakes are pressed...

With the LEDs, i'm sure they are all the same. They are probably messing up the circuit just like my wrong bulb did.... i'm not sure how you would fix this, since I don't know if they make dual leds??? if that makes sense