The bug

When an entity carrying a banner with a pattern has the glowing effect, the glowing effect is applied to the separate banner patterns as well, instead of only outlining the banner.

To reproduce

Ominous banner

1. Find a pillager outpost
2. Wait for patrol leaders to spawn
3. Ring a bell near them

Custom banner

1. Spawn a husk
2. Run

   /replaceitem entity @e[type=husk,limit=1,distance=..5] armor.head minecraft:blue_banner{BlockEntityTag:{Patterns:[{Color:4,Pattern:tt},{Color:5,Pattern:bts},{Color:3,Pattern:mc}]}}
   

3. Run

   /effect give @e[type=husk] glowing 10 1