All,

I've run across an interesting bug that I haven't seen before. In the
attached Metpost file, if I delete the last figure (beginfig(8)...endfig),
the file compiles. However, with beginfig(8)...endfig, the file gives this
error:

 [1] [2] [3] [4] [5]
[6] [7]
>> path
>> pen
! Not implemented: penoffset(path)of(pen).
<to be read again>
                   ;
pen_pickup_->...part.penoffset.left.of.currentpen;

pen_bot:=ypart.penoffset.r...
<to be read again>
                   ;
l.499   pickup pencircle scaled 2pt;

?

As the code in beginfig(8)...endfig is a simple copy and paste of the code
in beginfig(1)...endfig, this is perplexing to say the least. 

If in beginfig(8)...endfig, I replace the lines

  %draw pendulum length
  pickup pencircle scaled 2pt;
  draw A--E;
  pickup defaultpen;

with:

  %draw pendulum length
  draw A--E withpen pencircle scaled 2pt;

Now the file will compile.

This is strange indeed! Any ideas?