I have Shimano LX 580 shifters, about 3 months old. the rear derailleur has had a suspect shift since new. The shifts from smallest to second largest have the same "thumb travel", but the last "click" requires a bit further travel, to get the click!!! The problem is that, if you not sure which gear you are in, and you use the normal "thumb travel" for the bigest cog, it will shift up, then drop back!! If you treat each shift as though it were onto the biggest cog, then you jump 2 and come back to the selected one!!! Hope this makes sence, and someone can tell me if its normal, or faulty???