Updating step to achieve an uneven step ratio

Hello! I am currently working on an app where I'd like to set an specific distance. At distances longer than 1000m it doesn't really make sense to have it set on steps of 100m anymore, so then it would be better with steps of 500m, while on distances shorter than 1000m it would be nice to have the specificity of 100m steps.

Currently we are doing this by updating the step value based on the current value of the slider. However, this seems to sometime fail, and sudden changes to the value seem to reset the slider to it's starting value (500m).

I am posing this as a question since I have no idea of this is an bug or (more likely) that our implementation is borky. Is there a better way to implement an uneven stepping of the slider?