Negative subscriber count in User Agent when crawling

We’re building a feed aggregation service, and while building an integration for NewsBlur, I noticed that on one occasion the User Agent reported a negative subscriber count.

The full User Agent string was:
NewsBlur Feed Fetcher - -1 subscribers -… (Mozilla/5.0 (Macintosh; Intel Mac OS X 10_7_1) AppleWebKit/534.48.3 (KHTML, like Gecko) Version/5.1 Safari/534.48.3)

The request came in at 2014-09-25 17:52:06