That looks like scorch, when wet leaves get the sun on them the water acts as a magnifier and scorches the leaf tissue. I have a similar Acer which has lived in a pot for 24 years but always in a shady spot.

Erm, here's a bit of information for you, Landgirl 100 - I, too, believed the myth about sun on water droplets burning leaves, but its been disproved. I looked it up a while back and it turns out the original experiments were carried out by a bunch of Hungarian students, who used glass droplets instead of water droplets. The leaves burned in sun through the droplets - but when the tests were carried out again with water a few years later, no such burning occurred. Water and glass have a different refractive index, so damage cannot occur from water droplets on leaves.

The damage on that leaf in the top picture looks as if a caterpillar has emerged (especially if leaves were stuck together) and left the holes behind, but check the backs of the leaves and stems for any evidence of scale infestation. I can't really tell what the white deposits on the lower leaves pictured is - bird droppings? Paint?