grid_view_delete_cells does need to clear, GitHub issue 1871.

grid-view.c

@@ -214,6 +214,7 @@ grid_view_delete_cells(struct grid *gd, u_int px, u_int py, u_int nx, u_int bg)
 	sx = grid_view_x(gd, gd->sx);
 
 	grid_move_cells(gd, px, px + nx, py, sx - px - nx, bg);
+	grid_clear(gd, sx - nx, py, px + nx - (sx - nx), 1, bg);
 }
 
 /* Convert cells into a string. */