We do not really need to clear the compatibility field. And applications like magma need it anyway.

src/core/task.c

@@ -330,8 +330,6 @@ void _starpu_task_check_deprecated_fields(struct starpu_task *task)
 				task->handles[i] = task->buffers[i].handle;
 				task->cl->modes[i] = task->buffers[i].mode;
 			}
-			task->buffers[i].handle = NULL;
-			task->buffers[i].mode = STARPU_NONE;
 		}
 	}
 }