Why does dmextract convert arcseconds to arcminutes when I use pset?

unix% pset dmextract  \
      infile='infile.fits[bin sky=ellipse(161.18d,-59.71d,2.56",1.71",34.40)]'

unix% plist dmextract

Parameters for /home/username/cxcds_param4/dmextract.par

#--------------------------------------------------------------------
#
# DMEXTRACT -- extract columns or counts from an event list
#
#--------------------------------------------------------------------
        infile = infile.fits[bin sky=ellipse(161.18d,-59.71d,2.56',1.71',34.40)] Input event file

This is a bug in the parameter interface, caused by the double quotes used to denote arcseconds. As a workaround, create a one-line stack as the input to the tool:

unix% cat stack.lis 
infile.fits[bin sky=ellipse(161.18d,-59.71d,2.56",1.71",34.40)]

unix% pset dmextract infile=@stack.lis

See ahelp stack for more information on how CIAO treats stack inputs.