I always hesitate giving this kind of advice as I am no species expert. I did have this problem a couple years ago and was told it was leaf burn...too much sun too fast. While the tree may tolerate full sun, if it has been inside all winter it's not used to the direct sun rays. I move my inside plants out to a shaded are for a few days, then under an area that has dappled sun, then finally full sun.

I have an elm that has been inisde all winter and was sending out shoots like crazy but with really long internodes so I wanted it to get more sun. I put it outside (we, too, were having a brief spell of warm weather ((40 high today!) and the growth all stopped immediately. Even in the shade the move was obviously a shock to the tree. The tree is fine, my point is that inside to outside is always a shock to the tree.

Earl