Want to play "What's eating my Rose Bush Leaves"?

I have what I believe is a "Blue Boy" rose bush and it seems to be progressing fairly well, but I've recently noticed that there are...SHAPES that seem to have been cut out of the leaves. Now I say shapes because they're not exactly "holes", they aren't round - rather they seem to follow a path of the leaves veins to form more of a "window" shape.

I know the "blue" roses are pretty susceptible to black spot and I have a milk mixture that I've started using & is at the ready in the fridge for reapplication, but from what I know these window shapes aren't a symptom of black spot.

I've also noticed quite a few of what appear to be carpenter bees (possibly bumblers but I've never really gotten close enough to be sure), but the only mention I can find on bees making holes in rose leaves talk about round holes.

I haven't noticed any pests on the bush, nor under it's leaves (but I'm still kind of new to roses and don't always know exactly what to look FOR).

Like I said, the plant as a whole seems to be flourishing just fine, good colored leaves, strong new buds. But no explanation as to what's causing the windows on the leaves.