1. Install 5.11 beta3 without 'Sources' component.
2. Get a feeling that you need 'Sources'.
3. Go back to installer and select 'Sources'.
4. Wait till is finished.
5. Qt Installation is gone (no qmake, no toolchains, no libs), only 'Src' is still there
6. Go back to installer to install toolchains, installer claims is still there, but it is not.
7. You have to uninstall everting and install it again to have working env.

Please note the same will happens if you selected for example msvc2015, and later you want to add msvc2017. Installer keeps removing things it should not.