Funny, I think I had a similar issue with my DX today (altough I have to admit that I didn't fully read your post..)
Turns out my problem was sticking the cable in a different USB hole,
Had it in the front and as soon as I tried to copy something to the kindle (in my case the update from amazon) it disconnected.
Put it in a USB hole in the back - no problems.I figured it got more power from the back or something.
So maybe this helps.
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