The bug
Programmer Art contains some texture files for blocks which are exact visual duplicates of the current versions of those textures. It appears that Programmer Art is only intended to contain texture files for block textures which have changed since 1.13. This duplication means that applying Programmer Art on top of another resource pack which is itself on top of the vanilla resources will have the corresponding textures in the middle custom resource pack overwritten, which should not happen.
Affected texture files
The following block texture files in Programmer Art are visually identical to the ones from vanilla:
grass_block_side.png
sugar_cane.png
How to fix
Delete these texture files from the Programmer Art resource pack.
Further notes
The following does not appear to have any gameplay impact, but Programmer Art also appears to contain pointless duplicates of several mcmeta files for animated textures, which should probably also be removed alongside the textures mentioned above as Programmer Art does not replace these textures:
fire_0.png.mcmeta
fire_1.png.mcmeta
kelp.png.mcmeta
kelp_plant.png.mcmeta
lava_flow.png.mcmeta
lava_still.png.mcmeta
nether_portal.png.mcmeta
sea_lantern.png.mcmeta
seagrass.png.mcmeta
tall_seagrass_bottom.png.mcmeta
tall_seagrass_top.png.mcmeta
water_flow.png.mcmeta
water_still.png.mcmeta
Linked issues
discovered while testing 1
Comments


Can confirm in 1.21.5.
I think this is a good thing and shouldn't be "fixed". The reason it's like that is because it's future proofing for in case any of these textures do get changed