Not to break your hope but I believe fixing the kissing mismatch (is this what you refer to as kissing bug?) is not even something correctable by the slider itself, but involving hacking Sims 3 animation database to tweak the script so 2 sims can match lips upon kissing. Shorter sim will probably have to tilt head upward while taller sim will tilt head downward. This may be a whole lot of works than just creating a custom slider.
However, if someone did go through the trouble to make one, I wouldn't mind having. For now, sims can kiss foreheads. It still look cute.
I work for a living, but I don't necessarily live for a working.
Delphy made one, I downloaded it a few days ago. It isn't a perfect fix for the kissing mismatch, but I'm really happy with the results. Thanks again to Delphy for all the work done to improve TS3. The filename is MTS_Delphy_1025943_SimHeight.rar. I'm trying to find it, but not having too much luck. I'll kep looking, and if I find it I'll edit the post and include the link.
I currently use Delphys Height slider it works very well. I editsim whenever lips dont match and make the the same height but if you don't want to do that for every smooching pair then there really is no fix. It was said before its an animation issue not a slider issue. Hope that helps.