grdmath [ERROR]: Cannot use -I together with -R<gridfile>

[anbj]

Very brief; I'll give more detail if necessary.

grdmath complains about giving -I when I never did.
grid.tif just contains a bounding box in UTM coordinates.

$ gmt grdmath -Rgrid.tif 0 = trash.nc

$ gmt grdmath -Rgrid.tif 1 trash.nc ADD = trash.nc
grdmath [ERROR]: Cannot use -I together with -R<gridfile>

[joa-quim]

I don't think this is a bug. When when use -R, we are setting both the region and the increment.