commit https://github.com/vim/vim/commit/84dbd494dca599ecff05b2c2279d402c12e6d197 Author: Bram Moolenaar <Bram@vim.org> Date: Sun Oct 2 23:09:31 2016 +0200 patch 8.0.0021 Problem: In the GUI when redrawing the cursor it may be on the second half of a double byte character. Solution: Correct the cursor column. (Yasuhiro Matsumoto)

--- a/src/screen.c
+++ b/src/screen.c
@@ -765,6 +765,9 @@ update_screen(int type)
 	     * uses that. */
 	    gui.col = gui_cursor_col;
 	    gui.row = gui_cursor_row;
+# ifdef FEAT_MBYTE
+	    gui.col = mb_fix_col(gui.col, gui.row);
+# endif
 	    gui_update_cursor(FALSE, FALSE);
 	    screen_cur_col = gui.col;
 	    screen_cur_row = gui.row;