It's the second multidefine segfaulting. It does not seem to happen
Thanks for the report! Should be fixed in the latest git, please try.
You should get an error message saying "empty block" instead of a
segfault. Your script is a misuse of multidefine ("$msg" expands to
two words, so the second invocation of multidefine doesn't understand
what's going on), but that misuse wasn't properly caught.
Please give me a name (real if possible, else nickname) and e-mail
you wish to be credited with for the bug-report.