Slider moving forward correctly, but not backward

Greetings all

I am trying to create a timeline application using a slider.  Right now, I've only built out 2 slides as a prototype - a good thing, as I am having trouble with the slider.

I can move from one slide to the other just fine, but if I try to go backward, things mess up.  If I'm on the second slide and try to go to the first, the thumb part of the slider jumps back to position 2, even though the step 1 slide is visible.

To make the slider, I put the slider in the slide master, so it could be used by all slides, and put triggers for the slides there, too.

I've tried using the program in Review and in our LMS, and it is problematic in both.

Any advice would be truly appreciated!