When a plane gets a see-through hole, markings may be partially drawn on top of thin air. Pictured is the left side of a RAF BuffaloMK1, and there are gaping holes in the fuselage, with the interior and a small area of green grass visible, and the marking QV is fully drawn.
This is not exactly a bug, maybe more like a limitation of the engine. For comparison, a direct hit once completely removed a red star from a P-39N's wing, and it didn't look fake. Workarounds might be a lot of work, though, since markings are displayed in various places and sizes depending on plane, squadron, number and air force.
But there's more! The mirrors of P-51C-NT and MustangIII - you guessed it - don't block the sun.