artf2345
Rounded widget PtBasic loses its fill color (becomes transparent) in this combination of its resources : another fill color (Pt_ARG_FILL_COLOR) then transparent not flat fill (basic flags) Pt_ARG_HIGHLIGHT_ROUNDNESS greater then 0 Required color is drawn only in place of bevel border.
That is correct, here is the release note for PR24980: If you set a widget's Pt_ARG_HIGHLIGHT_ROUNDNESS resource to a nonzero value, the widget's gradient fill is now bypassed instead of remaining rectangular.