I did a test on Mac OS X (10.4.3).
With Apple's Browser Safari (2.0.2), there seems to be no problem at all.
With Firefox (old version: 1.0.7 ;-)), the map ist not shown at first (only grey background). After clicking e.g. the (+) Button to zoom in, a larger map with decoration (appropriate to the window size) is drawn. Afterwards, clicking the MapQuest link in a cache description immediately gives me the map each time I try it.
Rethinking that, it *could* be that with Safari the behaviour was the same (no map at first, but then it's ok). Maybe a cookie problem??
Regards,
Stefan (Ruhrteam)