This issue has the same name as one reported to the pygmt issues page, but it is the same problem in the GMT core:
gmt grdmath -R0/220/-30/90 -I1 -fg 0 1 RAND = t.grd
gmt grdimage t.grd -Rg -JW0/8i -B -png bad
which gives

Letting @GenericMappingTools/pygmt-admin know as well.