I don't know if this is the bug of Series 60 SDK or I misunderstand. that when you draw line with Pen Size which is not TSize(1,1) on GC, Either using DrawLine or DrawPolyline() will use EDrawModePEN mode to draw. No matter what other mode you set.
Does anyone know exactly what going wrong here ?
Exactly as documented in CGraphicsContext::SetPenSize description.