Steps to reproduce the issue

1. Setup Joomla with 4.0-dev branch.
2. Follow the installation instructions
3. When the installation is finished, do not press the "Delete installation folder" button.
4. Click on the "open backend" button

Expected result

The installation folder should remain.

Actual result

The folder is deleted without pressing the "delete" button.

System information (as much as possible)

I only noticed the error on Branch 4.0-dev, other versions were not tested.