When you say they are hidden, do you mean they are on the GM Layer, on a different page, or hidden by the line of sight/Dynamic Lighting? (And I assume this is when you are logged in as a player?) In theory if it's one of the first two (the GM Layer or on a different page), it shouldn't load in those resources via the Dev Tools (let me know if that's not the case). However, for things that you would be able to see via Dynamic Lighting but can't yet see, it does have to load in those resources ahead of time in order to render the page. In theory that's because if it's on a different page or the GM Layer the GM has to perform an action to show it to you, whereas with the Dynamic Lighting layer you could move your piece and see it at any time. Basically, it's a balancing act between sending you the resources you need to render stuff quickly that you could see at any time, versus not wanting to send the client resources for things until we absolutely have to. My only other thought is that most players/people aren't going to be opening up the Developer Tools. But if you're really, really paranoid about making sure that players don't see the graphic of an enemy ahead of time or something like that, just keep it on the GM Layer or a different page until you're ready to reveal it.
