It appears that some searchers may be seeing a limited number of organic search results when searching Microsoft Bing.
A WebmasterWorld thread has one searcher claiming his searches on Bing are only returning 5 results at a time. Another said he only is getting 8 organic search results. The rest are saying they see 10 results.
We've seen this before with Bing, where Bing shows random number of results. Back then, a Microsoft spokesperson told us that they are always testing - and by always - I assume also even now.
We're continually testing and experimenting on Bing in an effort to improve the user experience. We experimented with the number of answers for several months last year, and shipped the new format in June. In cases where there are answers (like a photo or video or news answer, we may provide a few more links to ensure there is right number of algo in addition to the answer blocks.
I personally do not see 5 results per page on Bing, but I can definitely believe some people are.
Forum discussion at WebmasterWorld.