JComponent sends painting through the BufferStrategyPaintManager. When the Graphics being painted to is not a screen graphics, this results in an un-needed double-buffering and the BSPM being marked out of sync until a full repaint of the root pane. This could be improved such that BSPM is only used for known paints to screen, or at least changed such that the buffer doesn't stay out of synch for so long.

See 6542106 that provides a fix for the case of painting to an image.