Autotune in Loiter mode, but get Althode mode when it's finished

I tried autotune in Loiter mode to tune only Yaw axis today, when autotune finished it will auto switch to althold mode, is this normal?
After I turn off autotune and turn on, it will back to Loiter mode.

Here is my log

There is no indication of mode change at the end of Autotune, it remained in Loiter.