There are 2441 pages beginning with A-J
There are 512 pages beginning with KX
There are 2921 pages beginning with Kx
There are 4752 pages beginning with L-Z
Testing: [[Special:myLanguage/Non Existing Page|Non Existing Page]] gives Non Existing Page as it should!
This is an old issue which I reported to Ingo and Nikerabbit as a serious nuisance, so perhaps it was fixed some time ago and I had forgotten. I've removed the Trello card. Thanks for pointing it out.