combining multiple geojson files w tsv and preserving property with topojson

combining multiple geojson files w tsv and preserving property with topojson

i'm trying to do many things w topojson… combine 2 geojson files w 1 tsv,
join on ELECT_DIV n NAME, promote that to the id, and keep 2012_POP from
the tsv.
here's the command i'm using:
topojson -o electorates.json -e 2012_oz_population.tsv --id-property
ELECT_DIV,NAME -p 2012_POP -s .0000005 --allow-empty --
electorates.geojson region.geojson
ELECT_DIV is in electorates.geojson. it is getting set as the ID on all
the features, but each one is not getting the proper 2012_POP from the
join with the tsv. however, at the top level, electorates and region are
getting the last value of 2012_POP from the tsv, so it's joining in some
way...
any ideas on what i'm doing wrong? do i need to do this in more than one
topo command?
thanks!