You might want to specify more info - version of EE? Version of Stash? Etc. Off the top of my head, i'm betting the issue is with your {if} statements, because those run in a deeply weird order in many versions of EE.

Well, then, there's definitely some kind of text-replacement routine running, either from a plugin or maybe an extension. Or possibly the actual field, if you're using something like wygwam?

Hm. I'm thinking. :)

Do you have any sort of replacement plugins surrounding the content? Like Low Replace, or Hacksaw, or CE String?

Check the above edit and see if it solves your problem; I have ZERO idea how this will interact with anything, it's a really basic answer that addresses only the one place I know a specific numeric check is being done. There might be others; I don't know.

GWCode Categories is also REALLY REALLY SLOW when you have large numbers of categories; it uses terribly inefficient queries.