patch 9.1.0015: i_CTRL-R- no longer works in replace mode

Problem:  i_CTRL-R- no longer works in replace mode
Solution: delete characters in replace mode before putting, add a test,
          add a bit warning into the documentation, that i_CTRL-R-P/O
          is not supported in Replace mode for now

fixes: #13792
closes: #13816

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_normal.vim b/src/testdir/test_normal.vim
index 90bedf1..38ad810 100644
--- a/src/testdir/test_normal.vim
+++ b/src/testdir/test_normal.vim
@@ -4181,4 +4181,4 @@
   bw!
 endfunc
 
-" vim: shiftwidth=2 sts=2 expandtab
+" vim: shiftwidth=2 sts=2 expandtab nofoldenable
diff --git a/src/testdir/test_registers.vim b/src/testdir/test_registers.vim
index f85e727..50f3910 100644
--- a/src/testdir/test_registers.vim
+++ b/src/testdir/test_registers.vim
@@ -946,4 +946,24 @@
   bwipe!
 endfunc
 
+func Test_insert_small_delete_replace_mode()
+  new
+  call setline(1, ['foo', 'bar', 'foobar',  'bar'])
+  let @-='foo'
+  call cursor(2, 1)
+  exe ":norm! R\<C-R>-\<C-R>-"
+  call assert_equal('foofoo', getline(2))
+  call cursor(3, 1)
+  norm! D
+  call assert_equal(['foo', 'foofoo', '',  'bar'], getline(1, 4))
+  call cursor(4, 2)
+  exe ":norm! R\<C-R>-ZZZZ"
+  call assert_equal(['foo', 'foofoo', '',  'bfoobarZZZZ'], getline(1, 4))
+  call cursor(1, 1)
+  let @-=''
+  exe ":norm! R\<C-R>-ZZZ"
+  call assert_equal(['ZZZ', 'foofoo', '',  'bfoobarZZZZ'], getline(1, 4))
+  bwipe!
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab