I believe this has to do with the execution order of code blocks when you submit your solution. The way I see it, the order goes from Preloaded -> Your solution -> Kata's test fixture. It seems that your own test fixture gets its own environment, unaffected by the Preloaded code block.

Yes, it is disabled. I'm not sure why it would be enabled when you're running your own tests. Sounds like a site bug to me.