https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66578
--- Comment #6 from vehre at gcc dot gnu.org --- c= a(:) works because there is no additional array descriptor inbetween. The (new) allocate gets its own temporary array descriptor for the source= expression, which in turn has incorrect bounds in it. The arrayspec is an AS_DEFERRED which is then used to generate the temporary array descriptor and defaults to a lower bound of zero, where all the miserable things begin with.
