patch 7.4.1421
Problem:    May free a channel when a callback may need to be invoked.
Solution:   Keep the channel when refcount is zero.
diff --git a/src/eval.c b/src/eval.c
index db9c6b7..0db6cfa 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -7745,8 +7745,8 @@
 
 #if defined(FEAT_CHANNEL) || defined(PROTO)
 /*
- * Decrement the reference count on "channel" and free it when it goes down to
- * zero.
+ * Decrement the reference count on "channel" and maybe free it when it goes
+ * down to zero.  Don't free it if there is a pending action.
  * Returns TRUE when the channel was freed.
  */
     int
@@ -7754,7 +7754,7 @@
 {
     if (channel != NULL && --channel->ch_refcount <= 0)
     {
-	channel_free(channel);
+	channel_may_free(channel);
 	return TRUE;
     }
     return FALSE;