Changing "c == '@'" to "c == '@' && !want_attributes" in line 10145 of
subst.c seems enough to fix it.
--
konsolebox
diff --git a/subst.c b/subst.c
index 251eafaf..9ee816e0 100644
--- a/subst.c
+++ b/subst.c
@@ -10142,7 +10142,7 @@ parameter_brace_expand (char *string, size_t *indexp, int quoted, int pflags, in
/* All the cases where an expansion can possibly generate an unbound
variable error. */
- if (want_substring || want_patsub || want_casemod || c == '@' || c == '#' || c == '%' || c == RBRACE)
+ if (want_substring || want_patsub || want_casemod || c == '@' && !want_attributes || c == '#' || c == '%' || c == RBRACE)
{
if (var_is_set == 0 && unbound_vars_is_error && ((name[0] != '@' && name[0] != '*') || name[1]) && all_element_arrayref == 0)
{
