https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85363
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> --- That implemented the rule that aggregates can't have NSDMIs. It started working in C++14 mode with r216750, which implements the C++14 rule that aggregates _can_ have NSDMIs. So the problem seems to be when it's an aggregate.