Posted: 22/08/2015 at 09:29
One of two things - thirst makes acers lose their leaves or turn crispy and start curling. The other possibility is an illness that can strike at acers. I can't remember what it's called but the acer struggles to get going but, with food and watering, does well for a while but then loses its leaves.
I would try repotting with fresh, John Innes 3 compost and remove the top layer of soil and any fallen leaves. Give it a good drink and then leave it in a shady, frost free spot out of the wind and wait and see if it recovers next spring. Wind really dessicates their fragile foliage so you'll need to water it more than you'd think to counteract moisture loss.