User reported that performance was slowed with the experimental map because the map image tiles are not cached.
Pragma no-cache
Expires [Date and time the image was sent]
Cache-Control max-age=31536000, must-revalidate

I looked into the imap files and how they are created. One php file generates this:

header("Pragma: no-cache");
header("Expires: 0");

and another generates this:

header("Expires: " . date( "D, d M Y H:i:s GMT", time() + 31536000 ));
header("Cache-Control: max-age=31536000, must-revalidate" );

I haven't worked out exactly how the machinery works, but those must be the files involved. JJ confirmed that the terms of use "prohibits further reproduction of these images in any form under any circumstances" so she and David felt that preventing caching was required by those terms.