Proposed resolution:

Change the specification of do_allocate() ([mem.res.private] p2+p3) as follows:

Returns: A derived class shall implement this function to return a pointer to allocated storage (3.7.4.2) with a size of at least bytes, aligned to the specified alignment. The returned storage is aligned to the specified alignment, if such alignment is supported; otherwise it is aligned to max_align.

Throws: A derived class implementation shall throw an appropriate exception if it is unable to allocate memory with the requested size and alignment.