If you look at most banner patterns, their item forms show the pattern in black. The problem comes with "Bordure Indented" and "Field Masoned" banner pattern items because those two, instead of showing their patterns in black, are instead showing the inversion of themselves in black: 
 - Bordure indented should show borders, instead shows the inside of the banner
 - Field Masoned should show bricks, instead shows the "filling" lines between the bricks

This is also a problem in Bedrock - MCPE-184864, it's where this inconsistency actually originates from.