I don't know the thread you speak of, but I noticed the Finder is sometimes way behind on what actual free space is available. I tend to use Activity Monitor to get the correct amount.
My Guess is you have been creating files in the background that are then taking up drive space. When you go to delete something the Finder is then updated to reflect the deleted files but also the files you have added since the last time it was updated. If the files you have added are bigger then the ones being deleted, you can see how space would go down.
My guess anyways!