Index: src/normal.c
===================================================================
--- src/normal.c	(revision 57807)
+++ src/normal.c	(working copy)
@@ -7393,6 +7393,8 @@
 	}
 	else
 	{
+	    if (Unix2003_compat && cap->cmdchar == 'S')
+		beginline(0);
 	    if (cap->count0)
 		stuffnumReadbuff(cap->count0);
 	    stuffReadbuff(ar[(int)(vim_strchr(str, cap->cmdchar) - str)]);
@@ -8318,6 +8320,8 @@
 
     if (!checkclearopq(cap->oap))
     {
+	int undo_offset = 0;
+	int save;
 #ifdef FEAT_FOLDING
 	if (cap->cmdchar == 'O')
 	    /* Open above the first line of a folded sequence of lines */
@@ -8328,11 +8332,21 @@
 	    (void)hasFolding(curwin->w_cursor.lnum,
 						NULL, &curwin->w_cursor.lnum);
 #endif
-	if (u_save((linenr_T)(curwin->w_cursor.lnum -
+	if (Unix2003_compat) {
+	    beginline(0);
+	    /* Undo of 'O' leaves cursor above the deleted line */
+	    if (cap->cmdchar == 'O' && curwin->w_cursor.lnum > 1) {
+		    undo_offset = 1;
+		    curwin->w_cursor.lnum--;
+	    }
+	}
+	save = u_save((linenr_T)(curwin->w_cursor.lnum + undo_offset -
 					       (cap->cmdchar == 'O' ? 1 : 0)),
-		   (linenr_T)(curwin->w_cursor.lnum +
+		   (linenr_T)(curwin->w_cursor.lnum + undo_offset +
 					       (cap->cmdchar == 'o' ? 1 : 0))
-		       ) == OK
+		) == OK;
+	curwin->w_cursor.lnum += undo_offset;
+	if (save
 		&& open_line(cap->cmdchar == 'O' ? BACKWARD : FORWARD,
 #ifdef FEAT_COMMENTS
 		    has_format_option(FO_OPEN_COMS) ? OPENLINE_DO_COM :