Copy Pasting a Rotation in skeleton results in buggy numbers

I’m currently going through the bones of skeleton A, copying their rotations and pasting them in skeleton B.
Both are UE4 mannequins, but one of them has a different retarget pose, which is why I’m doing this.

However, when I copy the rotation of a bone of skeleton A, then paste it in the same bone’s rotation of skeleton B, the numbers change with each paste I do, sometimes getting very close to the actual numbers, sometimes not at all. The most suspicious behavior is that sometimes a paste 4x, one after another, results in 4 different rotations. How and why?

I also noticed that most times, the numbers get closer the more often I press “paste”; as if the copy paste mechanic didn’t simply copy and paste values, but somehow calculates values closer to the wanted (the copied) numbers. It’s very annoying pressing 4x “paste” just to get similar numbers. This is copy & paste. I get that the lowest decimals might be different thanks to rounding errors, but whatever this is right now is not really acceptable.

Have you succeeded at solving the problem?