The movement of the slider bar can appear to return to its previous setting once it has been re-set.   After setting the slider to a value, it will read the actual value from the PLC, this value is then shown in the slider, resulting in the slider moving from the re-set value to the old value, the slider then starts to move towards the re-set value. This actually better reflects the current value in the PLC, but can be undesirable.
In this case de-select the "Immediate update on slide move" option in the slider wizard to prevent it.