Problem when unmounting child platforms

Summary

There is a problem in the unmount-mode for child platforms.

Steps to reproduce

Create a device
Create 2 platforms ("parent", "child")
Create a configuration
Mount "parent" platform in configuration with open end
Mount "child" platform and device below "parent" platform with open end
Go into un-mount mode
Select the child platform

What is the current bug behavior?

We should be able to directly unmount the "child" platform

What is the expected correct behavior?

The form is disabled on the first selection of the "child" platform. When clicking on the device & again on the child platform the form gets active. When clicking on the parent platform (that can't be unmounted due to the other mounts that are still active) it shows the validation message ("The selected platform still has mounted platforms or devices. Please unmount them first"). The validation message here is ok. But it stays when selecting the child platform - which again has a disabled form.

Some logs and/or screenshots

Hierarchy:

First click on child platform in un-mount mode:

After clicking on the device & then again on the child platform:

After clicking on the parent platform and again on the child platform:

Possible fixes

ToDo's

Bug reproduced
Cause found
Bug fixed

Context of the discussion in the merge request:

The following discussion from !434 (merged) should be addressed:

@maximilian.schaldach started a discussion: (+1 comment)

This looks good so far.

I was curious if a similar message would appear if you do the same setup as described in the issue's description and then try to unmount the root platform, because this the exact same case is in my understanding.
The message appearing when doing so is The selected platform still has mounted platforms or devices. Please unmount them first.
Good so far, however, the message when trying to unmount the child platform is the exact same one and I am not able to unmount via the "Unmount form". Maybe you can check if this might be a bug here, if so, this belongs to a separate issue.