Currently, ikiwiki indexes the "title" and "link" fields of a page using the prefix "Z". This is incorrect. "Z" is for stemmed terms, which xapian inserts itself. Furthermore, the custom field "LINK" should use the "X" prefix. (This is according to the xapian-omega documentation.)

I have a patch that fixes this. Once it is applied, the wiki should be rebuilt to fix the search index.

What problems does the current behaviour cause? Consider the tags page. ikiwiki indexes the term "ZStags" for its title. xapian stems this and also indexes "ZZStag". (Notice the additional "Z".) Now when searching for "title:tags", xapian stems this and searches for "ZStag", and so only finds pages which were indexed by ikiwiki with "ZStag" (i.e. those pages with the singular "tag" in the title).