InlineTextBox should setStrokeStyle(SolidStroke) where appropriate, otherwise the old StrokeStyle will be used when drawing underlines for text.
Due to a bug in GraphicsContextCG (which fills rectangles to draw line strokes), this bug does not affect CG graphics, but does affect GraphicsContextCairo.
Created attachment 16834 [details]
I've just added context->setStrokeStyle(SolidStroke) in a few places as proof of concept. This may not cover all cases, and needs testing against the Mac port.
This was fixed with r41152 I believe although the workaround in GraphicsContextCairo should probably be removed.