patch 7.4.1896
Problem:    Invoking mark_adjust() when adding a new line below the last line
            is pointless.
Solution:   Skip calling mark_adjust() when appending below the last line.
diff --git a/src/misc1.c b/src/misc1.c
index 9fa8578..7969968 100644
--- a/src/misc1.c
+++ b/src/misc1.c
@@ -1425,8 +1425,11 @@
 								      == FAIL)
 	    goto theend;
 	/* Postpone calling changed_lines(), because it would mess up folding
-	 * with markers. */
-	mark_adjust(curwin->w_cursor.lnum + 1, (linenr_T)MAXLNUM, 1L, 0L);
+	 * with markers.
+	 * Skip mark_adjust when adding a line after the last one, there can't
+	 * be marks there. */
+	if (curwin->w_cursor.lnum + 1 < curbuf->b_ml.ml_line_count)
+	    mark_adjust(curwin->w_cursor.lnum + 1, (linenr_T)MAXLNUM, 1L, 0L);
 	did_append = TRUE;
     }
 #ifdef FEAT_VREPLACE
@@ -2861,7 +2864,10 @@
     void
 appended_lines_mark(linenr_T lnum, long count)
 {
-    mark_adjust(lnum + 1, (linenr_T)MAXLNUM, count, 0L);
+    /* Skip mark_adjust when adding a line after the last one, there can't
+     * be marks there. */
+    if (lnum + count < curbuf->b_ml.ml_line_count)
+	mark_adjust(lnum + 1, (linenr_T)MAXLNUM, count, 0L);
     changed_lines(lnum + 1, 0, lnum + 1, count);
 }