User blog comment:Rappy 4187/Technical Update: November 2, 2015/@comment-2112602-20151103080822/@comment-24473195-20151103113230

It is a known bug. Urls with special characters don't render properly and sometimes prevent "right" search results or block certain features.

In this particular case the difference between the pages is that the other ones were created a long time ago, and have not been changed recently.