When hovering over a link to en/wiki/Kiev (in /en/wiki/Hyman_Kaplan), "The population in July 2015 was 7006288797400000000♠2,887,974, making Kiev the 7th most populous city in Europe." appears, where there is "The population in July 2015 was 2,887,974 (though higher estimated numbers have been cited in the press), making Kiev the 7th most populous city in Europe." in the article.
I might have a few guesses as to the reason of the bug, but it does seem to be a problem on the hovercard's side.