Hi. The RS creates something weird when comparing different pages (try he:Special:diff/19354520/19357934, and see the url address with two NaN-s after slider opening). Btw, the wikEdDiff stops working at all.
So the RevisionSlider is not shown on SpecialPages, however Special:Diff redirects away from a special page to a regular diff page and thus the slider is still loaded here.
The titles of the two revision ids should be compared instead and only if they match the revisionslider should be loaded!