On my 05 I found condensation had got into the spring behind the gear position indicator plunger and the spring had failed. This caused a poor electrical connection from the gearchange shaft to the indicator sensor. Not only was it causing the neutral light to do what you have but with Tuneboy connected it was giving random gear indications so the ecu wouldn't know which map to use.
The sensor face had been worn badly by the spring loaded plunger, no oil gets up there, so I replaced the sensor, spring and pin/plunger and put a lot of grease on it.
No more problems with it after.
Easy job to do. LH rear of the engine, 2 bolts hold the sensor. Take it out, check face for wear, mine had a groove through all the electrical points and if you look with a mirror, in where the sensor fits, there is a small pin in a hole on the end of the gearchange shaft, check the spring, it may come out in 2 pieces.
Replacement is the best option if it's worn.
To remove the sensor completely tie some string to the wiring so you can pull the new wiring loom back in the same place, connections are behind the lh plastic triangular aux power socket panel.
Lubricate it well. Refit with sealant so water doesn't get past the rubber ring.