This allows the test case to succeed, and I think is what the indicated changeset intended.

diff --git a/src/casetab.c b/src/casetab.c
index 13bed64..5f3c8db 100644
--- a/src/casetab.c
+++ b/src/casetab.c
@@ -286,7 +286,7 @@ init_casetab_once (void)
       int c = ((i >= 'A' && i <= 'Z') ? i + ('a' - 'A')
               : ((i >= 'a' && i <= 'z') ? i + ('A' - 'a')
                  : i));
-      CHAR_TABLE_SET (up, i, make_number (c));
+      CHAR_TABLE_SET (eqv, i, make_number (c));
     }

   set_char_table_extras (down, 2, eqv);