A searcher reported a bug that Google confirmed in the Google Web Search Help forums saying that the country filter search tool doesn't work right.
If you search within a country specific Google property, such as at google.co.nz, under search tools, you'll see a country filter drop down to filter results only from "Country: New Zealand." But for some folks, that filter is not working.
Here is a screen shot showing the filter set but the results showing web pages from ccTLDs that are not co.nz:
AJ from Google commented on the thread confirming that Google will look into the bug:
Thanks bluequoll for escalating this, and thank you Vernita for the feedback! We are looking into this and will provide any updates as soon as we have any. Thanks!
Forum discussion at Google Web Search Help.