Background not erased for PhAB apps run under phDitto

My applications built with PhAB look fine locally, but
if run on a remote machine via PhDitto, their main window is
transparent, and shows the underlying desktop.

This even happens in PhAB itself, if I run PhAB remotely.
My “base window” as showing in PhAB is transparent when
seen over the net.

My base window has the default options, and a grey,
nontransparent fill color.

Presumably I have to set something to force drawing,
but what?

John Nagle
Team Overbot