I have Dura Ace 8/9 speed bar end shifters on my commuter. I'm using them with a 9 speed cassette, and they've worked great for over a month, about 200 miles.
You have to dismantle the shifters to install or remove. I've removed and installed these shifters at least 3 times since I've been trying to figure out which of my old handlebars to use (I have several, doesn't everyone?). I'm always careful and haven't broken or lost anything.
Each time, they have gone together just fine - it really isn't technically difficult. There's a couple of parts that have to fit with each other just right, but there's really only one way (as far as I can tell), so if you get it assembled the only way it fits, it works.
Each time I've reassembled them, it seemed straight forward and easy - I put them together, and they work, no big deal.
Last night I installed them on yet another set of handlebars. Same assembly procedure, nothing different, nothing visible broken or no parts lost. But, when I went to check out the shifting on the rear/right shifter, the indexing was all screwed up:
call the smallest cog #9, largest #1:
9-8 index perfect
8-7 index OK, but not great, seems to need adjustment
7-6 doesn't shift
next index goes from 7 not to 6 or 5, but seems to be a "mega index" (large throw between indexes) and go all the way to or 4. It's like 2 or 3 index stops are actually missing
4-3 OK, not great
I took it apart, looked at everything closely, and reassembled. No joy. I know how to adjust indexing and have always been able to adjust indexed shifters well.
What could be going on? I've switched to friction which works fine, but this has me stumped.