properties not being cleared properly?

[John W. Eaton]

Try running

  demo surfnorm
  demo stem

Although the surface in the surfnorm demo seems small to me, it
appears to be doing the right thing.  But the subsequent stem demo is
being added to the 3D surfnorm plot instead of generating a new 2D
stem plot.

I don't understand why this is happening, or what the correct fix is,
so I could use some help with fixing this problem.

jwe