Trying going to a page like this:
If you sort by a column header, for example Level Range, it only sorts the currently displayed results, which are fixed to be sorted by name. In other words, if a zone has more than 75 NPCs, you can't sort them all, only subsets. Sorting should sort the entire search result.
An easy workaround to this problem would be to increase the number of returned NPCs from a search to a higher number, like 500.