Mac does exactly the same thing, but he does it so that he can use the lead rope to rub his belly and chest when he is itchy! Vet saw him do it once and said he should be in a circus.
I found if I tied him really short, he still did it and it was really difficult to get him loose again, so I tend to tie him with a longer rope and just keep an eye on him. Since we have moved yards, the tie rings are mounted a lot higher and he doesn't seem to be able to get his leg over now.
We've had two big wooden posts sunk in concrete on the yard a horse width apart and we cross tye up on those anything that's remotley trouble some, so fat so good no problems at all in those. Oh and we use those ropes with a quick release clip which we put on bailer twine at the ring end and then the normal clip on the horses head coller.
I know people use them in other ways but this works for us.
What about cross tieing him? That way if he reared up then there's no ropes to get tangled in since they're either side of him (rather than 1 in front of him)?
Agree with AliBabe (sorry just noticed she's already said cross tieing) about getting on of those quick release ropes. We use these in the trailer, just in case.
Otherwise, you say its just when you leave him on his own - 1 of mine panicks if I even walk out of sight at home. But I do find tying him up outside so he can see the other horses better.