number of posts displaying in admin section

I just noticed that when I’m logged in and am in the posts admin section, the number of posts actually shown on each page is different than the post range displayed next to the pagination links.

To clarify, a list of only 15 of my 436 posts display at a time, but in the top right corner of the list, it shows a range of 20 posts being displayed (e.g. “Displaying 361-380 of 436”). I have no filters on, so it’s showing all dates and categories.

I have a few different installs of 3.0, and this is happening on all of them. Do you know what’s causing the discrepancy? Is this a known bug?

Thanks in advance!