commit https://github.com/vim/vim/commit/b7522a2f0ca6c970df37241c9e70024465d8596b Author: Bram Moolenaar <Bram@vim.org> Date: Sun Feb 21 17:20:55 2016 +0100 patch 7.4.1379 Problem: Channel test fails on Win32 console. Solution: Don't sleep when timeout is zero. Call channel_wait() before channel_read(). Channels are not polled during ":sleep". (Yukihiro Nakadaira)

--- a/src/misc2.c
+++ b/src/misc2.c
@@ -6239,6 +6239,11 @@ has_non_ascii(char_u *s)
     void
 parse_queued_messages(void)
 {
+    /* For Win32 mch_breakcheck() does not check for input, do it here. */
+# if defined(WIN32) && defined(FEAT_CHANNEL)
+    channel_handle_events();
+# endif
+
 # ifdef FEAT_NETBEANS_INTG
     /* Process the queued netbeans messages. */
     netbeans_parse_messages();