Eh.. but the collisions are still there for the parts that aren't updated.
Ashley , If you want to limit the use of the tilemap, you should force it to resize itself to avoid confusion. There is however the possibility that someone would want to update only a section of the tilemap- I don't think you should disregard that. This is an opportunity to make your product better.
It's mainly just odd that the tiles outside of the updated area remain visible, as well as their collisions- so why not their tile number be accessible as well? It just seems like an oversight. Something just isn't right with it. I also don't think it is good to just assume nobody will ever update just part of the tileset and expect the rest to go unused- that sort of thinking limits creativity.
edit: I guess I could make a plugin that loads in a section with offsets, etc.. I think I'll do that for now.