Unrendered banners take on form on new blocks placed

This is difficult to explain, but when a banner exists that is not rendering, any block update of placing will change the unrendered banners to look like the block placed.

See video for visual explanation
https://www.youtube.com/watch?v=PzV0WHb-P8c

All these issues were in the same chunk. Unsure if reproducible without excessive banners.