I have Shimano 9 speed bar end shifters. A week or so ago the RD shifter came loose and would have fallen out but for the shifter cable securing it. When I got the bike home I took the shifter off and tightened it (to the handlebar) and reassembled it. The next day when I rode I noticed it was not shifting well. In fact it was not only not shifting well it was friction shifting. This bar end can shift SIS or friction, though now it was set SIS mode but friction shifting. I realized that I must have reassembled it incorrectly. So when I got back home I took it apart again and reassembled it correctly.

(Like this https://www.flickr.com/photos/8130268@N04/5589524981)

However, it now shifts erratically. It sometimes slips into another gear when not shifted. The spaces between shift detents does not seem even. I have checked the cable and the housing. The derailleur appears OK. Anyone have any idea what is going on?
At this point I think the shifter is toast.