We just installed 2.52 on debian testing, and all edit links with symbols (including spaces) are coming up with empty text fields because the URL to the mdwn file is wrong.
For example, the existing page:
wiki/bugs/__39__Existing_Subject__39___vs.___39__Browse__39__/
displays the bug "'Existing Subject' vs. 'Browse'". But if we click 'Edit' on that page, we get:
wiki/ikiwiki.cgi?page=bugs%2F'Existing%20Subject'%20vs.%20'Browse'&do=edit
.. which of course opens with a blank edit box. Note that manually typing in the correct URL:
wiki/ikiwiki.cgi?page=bugs%2F__39__Existing_Subject__39___vs.___39__Browse__39__&do=edit
does work.
You need to rebuild your wiki on upgrade to 2.52. The old edit links looked like the first link above, and ikiwiki has changed so that it needs the new link above. To get those links on static pages, you need to rebuild the wiki, like the news says to.