Just started using Photo a couple days ago and am very impressed.
I've actually been drawing in it and it's lovely! Much better brush engine than Photoshop (20+ years PS user here).
However, when I go to merge two line art layers (pixel), the art from both disappear, leaving me with a blank layer.* I tried several times, even downloaded the 1.7 beta and no matter what, it disappeared.
Naturally I tried merging pixel layers of full photos: no problem there.
So maybe the amount on the layers is the problem? Though I can select all the line art information, and oddly, then fill it onto the layer I want in perfect fidelity. So I do have a workaround, but...
Any help in how I might merge layers and retain all the information would be appreciated. I am working on a Mac and have attached an example of the art I'm talking about.
*Additionally, when I try to add a Recolor adjustment to an art line layer, nothing happens.