(Just as an aside, believe it or not, it also displays the wrong time - it's
always out by 2 minutes.  I thought that accurate time keeping was important to
GPS units.)

This is a very common trait in Magellans.  http://www.gpsfaqs.org/faqs/magellan/explorist/explorist600/usage.html#time
 
I'm also the proud owner of an even older Magellan GPS 315 and that's exactly
the same...

I think the non-mapping ST and the 315  share DNA.  The yellow model always struck
me as a repackaged 315, that was cost optimized for service, as the case isn't
ultrasonically welded shut as the 315 is.