for some reason After Effects adds an oposite moving curve, and there is no point to remove it...
one of Ae's oddities that is refereed to as "The Boomerang Effect". watch this: AE Keyframe Boomerang Effect, Part 1 - YouTube
to fix it: you can highlight both keyframes where this movement occurs between and right click on one of them->keyframe interpolation (or Ctrl+Alt+K) and choose under spatial interpolation->linear.
to avoid it: make sure you set your preferences to default spatial interpolation to linear and avoid 95% of the chances this will happen again:
Nice! Thank You so much! I wouldn't ever guess the name for this to find a solution...
Sure Buddy. I remember this was on one of my first gotchas in this software. glad to spare you from more of its annoyance.