Someone mentioned inspecting the cables and housings for kinks or excess length. I'd take this a step further. I think you're going to have to replace your derailleur cable and housing with a brand that offers the least compression. Frame flex or cable tension problems are the source of most auto shifts. If you can't reduce frame flex then you're going to have to reduce cable stretch and the easiest way to do that is by encasing the cables in a housing that resists compression.
The bar end shifters are making matters worse (than down tube shifters, for example) because you're running considerably more housing and you're running it along the handlebars which are typically flexible to begin with.
Good luck.
Last edited by cale; 09-01-12 at 03:45 PM.