patch 7.4.2026
Problem:    Reference counting for callbacks isn't right.
Solution:   Add free_callback(). (Ken Takata)  Fix reference count.
diff --git a/src/ex_cmds2.c b/src/ex_cmds2.c
index c8980b4..2b2d635 100644
--- a/src/ex_cmds2.c
+++ b/src/ex_cmds2.c
@@ -1121,8 +1121,7 @@
     static void
 free_timer(timer_T *timer)
 {
-    vim_free(timer->tr_callback);
-    partial_unref(timer->tr_partial);
+    free_callback(timer->tr_callback, timer->tr_partial);
     vim_free(timer);
 }