When a Steam client downloads a resource from a Steam game server (like a .BSD [sic] map), the resource is first compressed to save bandwidth. An associated .ZTMP file is stored on the server so the resource won't need to be compressed again the next time a client requests it. If you change the resource you need to delete the associated .ZTMP file so that the next person who downloads is doesn't get the old copy instead of the changed resource file (Steam does not detect changed game resource files and recreate the .ZTMP file automatically.)
