Ralph,
    According to my sources the shift of reference from German to
Netherlands was in the 17th century.  The origin of the word is Germanic and
means "tribe" originally Teutons: the hoards that Rome feared.
    As to the pejorative connotation, how about Dutch treat (not a treat,
you pay your own way), Dutch Uncle (no relation at all), a Dutch defence (a
retreat of sorts) or Dutch reckoning (guess work).  They are all not what
they seem.  But where did all this come from?  Nethertheless, they did have
there 20 years of western world dominance.
Double Dutch anyone?
Best,
Leland