Automatic movement between keyframes

Good afternoon,
I have a question about a feature of Final Cut Pro X.
I am working on a movie and wants to move a small block using keyframes.
I placed an keyframe at 1:00:07 and another at 2:29:05.
Both keyframes have the position X: 0, and position Y: -850.0.
But between the two keyframes, the block moves. At 1:54:18, the X:0, and the Y at -822.9. There are no further keyframes between the two i mentioned.

I can put a keyframe at 1:54:18, but than he's going to move on both sides of the middle keyframe. So it does not help anything.

Does anyone know how I can fix this? I might use the wrong keyframes or something?

Thanks!

Sincerely.

I'll assume you're using a version of FCPX before 10.1.2 (or 3). This would be due to the keyframes being set to Smooth, rather than Liniar. One of the two most recent updates fixed the Smooth drifting oddly.

I'm using version 10.1.3.
But your solution solved the problem! Thank you very much!