ppchtex+pstricks wrong output

[Ricardo Sanchez Carmenes <carmenes@bioquimica.uniovi.es>]

Dear Hans and ppchtex users:

I am using some of your conTeXt modules from plain+pdftex
(not the whole package), especially the ppchtex modules.

ppchtex works beautifully with pictex, i.e., the following
simple sample file compiles correctly with pdftex:

%%%%%% CUT: ppch-ok.tex %%%%%%%%%%%%%%%%%%%
\input m-pictex
\input m-ch-en

\startchemical
  \chemical[ONE,SB13,DB7,Z0137][C,H,R^1,O]
\stopchemical

\bye
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

However, when I try to use ppchtex with pstricks instead of
pictex, the file compiles, but gives the wrong result, with
labels and bounds that should go on the top of the formula
printed at the bottom, and vice-versa. Besides, the labels
(or substituents) are then badly positioned with respect to
the bounds.

See the attached sample, that should, theoretically, give the
same result as above, after passing through tex->dvips->ps2pdf:

%%%%%% CUT: ppch-bad.tex %%%%%%%%%%%%%%%%%%%
\input pstricks
\input pst-plot
\input m-ch-en

\startchemical
  \chemical[ONE,SB13,DB7,Z0137][C,H,R^1,O]
\stopchemical

\bye
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

It looks like as if, somewhere, the ppchtex macro that places
bounds and substituents above or bellow, had a sign changed.
The same error arises when using pstricks+ppchTeX from latex.

Regards,
Ricardo.