Closest thing I can think of would be back in the day when colour palettes were small enough that paint had colour blends in its palette, if you filled with one of those, it didn’t treat that filled area as one colour so that you could fill it again with a different colour.

But I wouldn’t even call that a bug so much as a lack of feature. And it was kinda satisfying to fill one of those blended colours and then alternatively fill with the two colours that made the blend and watch it slowly creep out to fill the entire space. Lol I didn’t even realize I still had that memory in the archives.