before_tags and after_tags

Hi,

I noticed that the list of "Categories" (tags) shown in the 2nd column doesn't behave as expected after a blog post is edited after it's been published. This question isn't about that behavior, but it is about 2 lines of code that I noticed while trying to figure out that issue. What is supposed to happen in the two lines of code isn't clear to me. The two lines below look like the use the same logic, but I think they're supposed to be different. I might not understand what's happening at this point. Thanks again!

http://bazaar.launchpad.net/~jgoguen/gablog/trunk/view/head:/handlers/functions.py#L485
http://bazaar.launchpad.net/~jgoguen/gablog/trunk/view/head:/handlers/functions.py#L486

484
  if not property_hash["draft"]:
485
   before_tags = set(article.tag_keys)
486
   after_tags = set(article.tag_keys)
487
   for removed_tag in before_tags - after_tags: