I found the problem. It really does not like it when you try to create a style with any forward slashes in its name. This creates the following line in its attached PHP file of something like
"css" => "hot/cold_1234502805.css"
which is read as "hot" being a folder.
Moral of the story, for the time being, do not use forward slashes when naming styles. And apparently, the owner being nobody has nothing to do with it, since this is still the case for new files, but it works as long as you don't include that pesky forward slash.