Layer moving between keyframes with same position coordinates

I am tracking a text later at 2 different points in my edit - between these 2 points, the text layer needs to remain where it is as indicated in the coordinates below: 

Position 745.0 ; 434.0

However in between these 2 identital position coordinates, the layer moves up and down like a curve before going back to the same coordinates when reaching the next keyframe section.

No Ease In / Ease Out applied. Can someone think of anything that could make it move like that?