patch 9.0.1852: i_CTRL-O does not reset Select Mode

Problem:  i_CTRL-O does not reset Select Mode
Solution: Reset select mode on CTRL-O in insert mode

closes: #13001
closes: #12115

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_selectmode.vim b/src/testdir/test_selectmode.vim
index 6e2c369..bf1b52b 100644
--- a/src/testdir/test_selectmode.vim
+++ b/src/testdir/test_selectmode.vim
@@ -310,4 +310,15 @@
   bw!
 endfunc
 
+func Test_ins_ctrl_o_in_insert_mode_resets_selectmode()
+  new
+  " ctrl-o in insert mode resets restart_VIsual_select
+  call setline(1, 'abcdef')
+  call cursor(1, 1)
+  exe "norm! \<c-v>\<c-g>\<c-o>c\<c-o>\<c-v>\<right>\<right>IABC"
+  call assert_equal('ABCbcdef', getline(1))
+
+  bwipe!
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab