I decided to name the banners in my world, created in one of the Pre-Release versions as a warm ocean buffet world, then updated to 1.13. All the banners I have used have been added in 1.13. Normal, unnamed banners work fine, but named banners sometimes appear black when added, and disappear after re-logging. Old banners that I removed also reappeared.

I would upload pictures however it keeps giving me 'missing token' errors, and I don't have third party cookies blocked.