This is quite common, Google has been known to hide some back link information, In the example you gave it is giving you two very different values, it may be that you are going do a different Google dataset as you view more pages within the results and the information is simply not available on that server.

Google have certainly been making it more and more difficult to obtain decent back link information lately, there are good reasons for this, it used to be possible to locate almost all the back links for a competitor then request links from the same sources, by making it harder to locate this information it makes it a little bit harder to simply go after your competitions links.

Mack.

There's another factor here, in addition to what Mack mentioned. On many (even all) searches the initial ESTIMATE of the total number of pages in the set of search results (notice that it says "about") can be off by a major factor. This is because of the way Google splits up their data, sharding it across many different servers. The're no easy way for them to just grab an accurate number.

Google did make some changes last year to improve the accuracy on some of the special operators, especially "site:", but recently the estimates are all getting worse. I'm guessing this increased inaccuracy means that Google made another change in their back office infrastructure in recent times.

There's more information about Google's link: operator in this thread: Google link: operator FAQ [webmasterworld.com]. It's always available in the Hot Topics area [webmasterworld.com], which is always pinned to the top of this forum's index page.