According to 6.7.5.5.3 [basic.stc.dynamic.deallocation] paragraph 3,

If a deallocation function terminates by throwing an exception, the behavior is undefined.

This seems to be in conflict with the provisions of 14.5 [except.spec]: if a deallocation function throws an exception that is not allowed by its exception-specification, 14.5 [except.spec] paragraph 10 would appear to give the program defined behavior (calling std::unexpected() or std::terminate()). (Note that 14.5 [except.spec] paragraph 18 explicitly allows an explicit exception-specification for a deallocation function.)