The paintings aztec and aztec2 are both named "de_aztec" in the tooltips of pre-defined paintings found in the Creative inventory. This makes it impossible to distinguish them before placing them down.
Here are the strings in the en_us.json language file"painting.minecraft.aztec.title": "de_aztec","painting.minecraft.aztec2.title": "de_aztec"
I think this is intentional.
If you look at the wiki for "Painting", you can see that the original names are both "de_aztec". (though this might be misinformation)
Maybe the two paintings can be renamed to two different "de_aztecs" if Kristoffer decides to rename them.