Another user reports this is an issue on https://en.wikipedia.org/wiki/List_of_films_with_a_0%25_rating_on_Rotten_Tomatoes as well ... and looks like https://en.wikipedia.org/wiki/1%25_(song) has the same issue. This might a problem with pages with escaped entities in the title.

Seems like this specifically affects the Reference Tooltips gadget (which is enabled by default on English Wikipedia and some other wikis). There's no issue when using Reference Previews, perhaps the gadget needs an update?

This seems to be a pre-existing bug in ExpandRelativeAttrs::expandRelativeAttrs() that was exposed by the enwiki Parsoid Read Views rollout (T430194). This breaks footnote navigation and any gadget that parses the href (like Reference Tooltips) on pages with percent-encoded characters in their title.

In T431600#12103037, @HakanIST wrote:

This seems to be a pre-existing bug in ExpandRelativeAttrs::expandRelativeAttrs() that was exposed by the enwiki Parsoid Read Views rollout (T430194). This breaks footnote navigation and any gadget that parses the href (like Reference Tooltips) on pages with percent-encoded characters in their title.

Can you elaborate on this a bit? An example of an attribute value which is being incorrectly expanded would be very helpful.