[NTG-context] metafun and \input graph

When I try to run some plain MetaPost foo.mp file, which includes an \input graph command, through mptopdf, e. g. by the call `mptopdf foo.mp' fails. Check with texexec --mptex foo.mp shows ! Redundant equation. <to be read again> ; l.148 Ten_to0=1; Ten_to1=10; Ten_to2=100; Ten_to3=1000; Ten_to4=10000; These are redundant, since the lines appear first in mp-form.mp and then are again loaded from graph.mp. Is there a way to use mptopdf for conversion of plain/non-metafun MetaPost files, e. g. a switch for mptopdf? Greetings Hartmut