I guess the problem comes from the Perl debugger restarting itself via exec $0 ..., which is only emulated under Windows and thus quite unlikely to work at all. If you look in C:/Perl/lib/perl5db.pl, line 3296 (in my case, it was line 2800), there is the handling of the R letter/command. The line number and error refer to an error in perl5db.pl and not an error in your script.

The change in behaviour likely stems from changes in the C-code of POSIX.pm or Perl itself.