If there is one banner with the below patterns:

1.Per Bend Sinister

2.Per Bend

3.Per Bend Inverted

4.Per Bend Sinister Inverted

Then we put it on shield, then the patterns above will become upside-down.

Based on the information in the purple panel, we can know the pattern name texts can not match the actually patterns in banner, which means the mistake is in banner instead of shield. 

This is because in versions earlier than 1.15, banner patterns used one correct atlas image "banner.tga", however in MCBE 1.15, some banner patterns were incorrectly named when they were splitted in "vanilla_1.15" folder.

In "vanilla_1.15" folder:

The pattern file named "banner_diagonal_left.tga" should be renamed as "banner_diagonal_up_left.tga",

The pattern file named"banner_diagonal_up_left.tga" should be renamed as "banner_diagonal_left.tga",

The pattern file named "banner_diagonal_right.tga" should be renamed as "banner_diagonal_up_right.tga",

The pattern file named "banner_diagonal_up_right.tga" should be renamed as "banner_diagonal_right.tga".

I know the renamings will break some banner creations crafted in MCBE 1.15-now. I know the developers may have noticed this so they chose keeping the mistake and modified the crafting table recipes to match the mistake. Maybe developers will go on, rename the correct shield pattern files to keep the mistake.

But I really do not think this was a good idea. For texture pack creators, when they convert a Java resource pack into Bedrock, then they will roughly ignore the mistake and will not follow the "vanilla_1.15" to keep it, and this usually leads to bigger trouble.

Please bring back the correct image names, no keeping the mistake! We have to make a better choices, don't we?