Remember Easter's Amazon Fail?
A person has come forward and claimed that they exploited Amazon's "Report as inappropriate" feature with a bit of a cross-site-scripting to get many thousands of users to unknowingly and unwittingly report a large list of titles as inappropriate, removing their sales ranking and excluding them from search results.
Amazon have yanked the feature during the fixup process which makes the story quite a bit more credible.
All in all 57,310 items were affected. Not just gay-themed books, but "a number of broad categories such as Health, Mind & Body, Reproductive & Sexual Medicine and Erotica."
Amazon refers to this as a "ham-fisted" cataloging error, which doesn't feel like it holds water. Someone was working on the Amazon databases over the Easter Weekend (a time when Amazon says it didn't have anyone to respond to the problem), and decides to classify most items (but apparently not all) that are tagged gay/lesbian as porn?
That doesn't seem very likely, to be honest.