Google admitted to a bug causing some webmasters to show a deflated number of links within the Google Webmaster Tools link report.
There were several threads at Google Webmaster Help dating back to August 5th with complaints. In a few, Susan Moskwa updated these webmasters that there was a limited bug effecting some webmasters.
Susan explained:
Hey folks, we did have an issue that caused some users' backlinks numbers to drop earlier this month. It should now be resolved. Thanks for letting us know about your experiences -- it helped us to track down the problem.
Webmasters have confirmed the links are not being reported accurately in Webmaster Tools.
Forum discussion at Google Webmaster Help.

Comments:
Silviya Howe
08/20/2011 01:48 pm
Thank you fo this update
SEO Professionals
08/23/2011 11:47 pm
There are a plethora of webmaster tools on the Internet to help webmasters in bettering their websites in a variety of ways; however, let's face it, we are going to be mainly concerned with webmaster tools, tips and tricks that help us achieve optimal standings in the search engine results pages, or SERPs, specific to Google.