https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64578
--- Comment #1 from Damian Rouson <damian at sourceryinstitute dot org> --- P.S. For the submitted case, a simple workaround is to switch the source allocation to an assignment. That simple workaround is an option in the intended application code, wherein the derived type component is also an unlimited polymorphic variable.
