That sounds like baby slug damage. They just haven't dissolved it all the way through.

Sounds like sun burn to me....give it more water.
Linda C

I had this same exact damage on my Daybreak, and to my surprised, I found a small green inch worm type creature just playing around where the damage occured. Since I removed and killed it, there has been no continued damage.

Ah yes, there are some sawflies and other caterpillars that will do that too! I forgot about those. They are often found on the back of the leaves.

I really do not think it is slug damage. The "holes" are just too different. Besides so far the slugs have been killed off. We are inundated with moths this summer. I would believe a worm or something, I have seen some different bugs this year, as well as chomp marks on the edges of some stuff. Maybe I will go spray some ammonia just in case. I wonder if it works on all soft skinned bugs? It should.

Arcy, I think I think I think ammonia only works on slugs because they're mollusks and they slime themselves to death. It may annoy other pests but not get rid of them.
But let us know how they react. How ever did someone discover ammonia killed slugs? Brilliant!