This might be a bug, e.g. when searching for
[wpf] answers:0 the ones and zeroes will be highlighted in the question previews:
Edit: As Arjan pointed out this is not restricted to search options which actually contain numbers.
This will be fixed in the next build, the issue was that behind the scenes the term highlighting (vector based) was grabbing up the advanced search options behind the scenes, such as the deleted and post type filters (usually 0 and 1, respectively).
It'll now keep a reference to the original Lucene query for highlighting before it's joined to the boolean master, rather than the overall query which obviously had some unwanted friends in there.