A tile was kept while the pattern's own art, tile and tiling were the ones it
was drawn from. Art that shows a symbol, is painted with another pattern or
holds an image or type doesn't change when those do, so the pattern kept
drawing the old symbol (in every renderer on the thread: the tiles are
shared). Such a tile now also remembers the document's pattern and symbol
art, image pixels and fonts, and is drawn again when they differ. A raster
effect on an object painted with a pattern reads all of that too, as one on
a symbol instance does.