This is far more likely to be a proxy issue than anything else. As good as public proxies can be if you are on a budget they are not as reliable as private proxies and will only allow you to use one search engine rather than both Google and Yahoo.
Since the number of Google proxies has dropped so much from how many were available just a few months ago NHSEO is currently relying on Yahoo for its searches. As Yahoo gives less results than Google you will not get as many results.
As I have stated previously (so I won't go into depth here about it) if the search results are returning pages on the same domain as other pages that are already in the database or previously posted to it will discard these pages so the search itself is likely returning lots of targets but the same ones that have already been posted to.