How about a picture of the bar where the cable slide thingy goes back and forth? That definitely is the wrong throttle tube and it probably doesn't fit on correctly in the first place. Probably loose so it only catches the cable slider sometimes. Well the bar definitely looks worn out from being bent. The are impossible to make them straight again and it would just look old anyways.
Here is an eBay auction that looks like the correct bar. It's a reproduction but a nice bend with the correct sliding cable slot for a throttle tube. Maybe your cable slide cut in the bar is worn out causing the cable to slip in the tube?
http://cgi.ebay.com/ebaymotors/HONDA...Q5fAccessories