Shimano DA Di2 rear derailleur is ghost shifting!

[Johnny Bravo]

history: 2 years old external wired DA Di2 installed on a Scott Addict R2
bike used almost daily, 30-80mi/day (depending on training schedule)
for the last 30 days I haven´t cleaned it up and the bb area (and wires) is very very very dirty (dry mud, it´s been raining sometimes)

2 days ago I noticed something was wrong, but it happened only 3-4 times and then stopped
but today the problem showed up frequently and I could replicate it at home
I thought it could be the battery, but I charged it and the problem is still there

here´s what´s happening:
everytime I shift the RD, it moves the chain to the next sprocket correctly - BUT after a few seconds, the junction box blinks red twice and then the derailleur moves by itself again in the direction I had shifted before (up or down) - causing another (unwanted) shift...
my RD is ghost shifting!!!

I would really appreciate some help here...

[Juanmoretime]

Sorry, I couldn't help myself.

[pritchet74]

Whoa. Weird. No ideas but I would love to heard the outcome. So you have a second wiring harness you can use to see if that solves the problem? If not and you wanna try that out I have an extra one.

[Johnny Bravo]

here's a video of the malfunction:

http://www.youtube.com/watch?v=QrIY0hm2RBw&feature=plcp

Despite Shimano International says Dura Ace components have a 3-year warranty, Shimano Brasil refused to take care of the problem - and claimed that the warranty is for 1-year only... go figure...

[pritchet74]

Are you in Las Vegas or Brazil?

[Johnny Bravo]

was living in vegas, now i'm in brazil

but if someone in the US can help with the warranty, i will gladly send the groupset by mail

[Johnny Bravo]

btw, i tested it with a second wiring harness and the issue was still there.
also connected to inverted shifters and tried FD alone and RD alone - RD kept showing the same behaviour...

one more ridiculous detail: neither Shimano Brazil, nor the biggest authorized shimano dealers in Brazil have one single unit of Di2 system checker!
i called each one of them...

[pritchet74]

That's just sad. Since I will probably be getting a 2nd set of Di2 derailleurs as a backup set I should get one of those system checkers....