In my texture pack, it won't add more than 1 painting per size group to the texture pack, leaving the rest of the paintings the default. I'm not sure what's happening here, but I'd like to have all my paintings in a pack, not just a handful.
The overall size of the texture pack is 16x, but I've upscaled the kz.png file's resolution to 64x because it didn't look good enough to me.
However, when testing the pack in Minecraft it looks like the high-res paintings are indeed high-resolution and the size they are supposed to be, but the default paintings are still 16x resolution and they don't appear smaller.
I hope this gets fixed soon so I won't have to specifically slap in a hand-made kz.png file just for the sake of the pack's completeness.