I keep noticing this type of floating effect on only certain key frame animations i create,
it's wierd, if i key frame the postion of a picture it will add a swing effect, i.e. it goes from 1 point to the other with increasing then decreasing the x co-ordinates
The position X point is set to 720, the next point is also 720, but for some reason it decides to go down to 601 in between the 2 key frames,
No keyframe interpolation style is given, had a simular issue in after effects with interpolation styles
Select the keyframes that are misbehaving, right-click on one of them, and select Spatial Interpolation > Linear. That should straighten out the animation. If not, check that you don't have an errant keyframe parked very close to another, e.g. one frame before your target keyframe.