1 files changed, 16 insertions, 14 deletions

diff --git a/src/xdisp.c b/src/xdisp.c
index c56cffa951d..a82736ccd18 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -9788,11 +9788,13 @@ try_window_reusing_current_matrix (w)
       
       /* Display up to a row that can be reused.  The variable
          last_text_row is set to the last row displayed that displays
-         text.  */
+         text.  Note that it.vpos == 0 if or if not there is a
+         header-line; it's not the same as the MATRIX_ROW_VPOS!  */
       start_display (&it, w, new_start);
       first_row_y = it.current_y;
       w->cursor.vpos = -1;
       last_text_row = last_reused_text_row = NULL;
+      
       while (it.current_y < it.last_visible_y
              && IT_CHARPOS (it) < CHARPOS (start)
              && !fonts_changed_p)
@@ -9804,6 +9806,7 @@ try_window_reusing_current_matrix (w)
          have at least one reusable row.  */
       if (it.current_y < it.last_visible_y)
         {
+          /* IT.vpos always starts from 0; it counts text lines.  */
           nrows_scrolled = it.vpos;
           
           /* Find PT if not already found in the lines displayed.  */
@@ -9847,8 +9850,8 @@ try_window_reusing_current_matrix (w)
           run.current_y = first_row_y;
           run.desired_y = it.current_y;
           run.height = it.last_visible_y - it.current_y;
-          if (run.height > 0
-              && run.current_y != run.desired_y)
+
+          if (run.height > 0 && run.current_y != run.desired_y)
             {
               update_begin (f);
               rif->update_window_begin_hook (w);
@@ -9867,13 +9870,14 @@ try_window_reusing_current_matrix (w)
           
           /* Disable lines not reused.  */
           for (i = 0; i < it.vpos; ++i)
-            MATRIX_ROW (w->current_matrix, i)->enabled_p = 0;
+            (start_row + i)->enabled_p = 0;
           
           /* Re-compute Y positions.  */
-          row = MATRIX_FIRST_TEXT_ROW (w->current_matrix) + nrows_scrolled;
           min_y = WINDOW_DISPLAY_HEADER_LINE_HEIGHT (w);
           max_y = it.last_visible_y;
-          while (row < bottom_row)
+          for (row = start_row + nrows_scrolled;
+               row < bottom_row;
+               ++row)
             {
               row->y = it.current_y;
 
@@ -9886,13 +9890,11 @@ try_window_reusing_current_matrix (w)
                 row->visible_height = row->height;
               
               it.current_y += row->height;
-              ++it.vpos;
 
               if (MATRIX_ROW_DISPLAYS_TEXT_P (row))
                 last_reused_text_row = row;
               if (MATRIX_ROW_BOTTOM_Y (row) >= it.last_visible_y)
                 break;
-              ++row;
             }
         }
 
@@ -9948,7 +9950,7 @@ try_window_reusing_current_matrix (w)
       
       /* Find the row starting at new_start, if there is one.  Don't
          reuse a partially visible line at the end.  */
-      first_reusable_row = MATRIX_FIRST_TEXT_ROW (w->current_matrix);
+      first_reusable_row = start_row;
       while (first_reusable_row->enabled_p
              && MATRIX_ROW_BOTTOM_Y (first_reusable_row) < yb
              && (MATRIX_ROW_START_CHARPOS (first_reusable_row)
@@ -9980,10 +9982,12 @@ try_window_reusing_current_matrix (w)
       /* Start displaying at the start of first_row_to_display.  */
       xassert (first_row_to_display->y < yb);
       init_to_row_start (&it, w, first_row_to_display);
-      nrows_scrolled = MATRIX_ROW_VPOS (first_reusable_row, w->current_matrix);
+      nrows_scrolled = (MATRIX_ROW_VPOS (first_reusable_row, w->current_matrix)
+                        - start_vpos);
       it.vpos = (MATRIX_ROW_VPOS (first_row_to_display, w->current_matrix)
                  - nrows_scrolled);
-      it.current_y = first_row_to_display->y - first_reusable_row->y;
+      it.current_y = (first_row_to_display->y - first_reusable_row->y
+                      + WINDOW_DISPLAY_HEADER_LINE_HEIGHT (w));
 
       /* Display lines beginning with first_row_to_display in the
          desired matrix.  Set last_text_row to the last row displayed
@@ -10031,10 +10035,9 @@ try_window_reusing_current_matrix (w)
 
       /* Adjust Y positions of reused rows.  */
       bottom_row = MATRIX_BOTTOM_TEXT_ROW (w->current_matrix, w);
-      row = first_reusable_row;
       min_y = WINDOW_DISPLAY_HEADER_LINE_HEIGHT (w);
       max_y = it.last_visible_y;
-      while (row < first_row_to_display)
+      for (row = first_reusable_row; row < first_row_to_display; ++row)
         {
           row->y -= dy;
           if (row->y < min_y)
@@ -10044,7 +10047,6 @@ try_window_reusing_current_matrix (w)
               = row->height - (row->y + row->height - max_y);
           else
             row->visible_height = row->height;
-          ++row;
         }
 
       /* Disable rows not reused.  */