Bends are inaccurate for some reason...

I have a note with a bend on it, that starts 4 semitones up, then goes all the way back down to 0 in about one fourth of the time. So I have a point at {x=0,y=8} and a point at {x=3,y=0} and a point at {x=12,y=0}. In order to make it sound right, though, I have to set the tuning to about -30.00.

I have an example file now. The bends seem to be accurate enough if you use whole notes, but perhaps the short duration and/or the portato messes things up? Either way, it is something that should be fixed, I would say.