Qt Maintenance Tool error when run without root

Step to reproduce (On Linux):
1) Run Qt online installer as root and install some old version of Qt Creator (eg. 4.8);
2) Run Maintenance Tool installed together with QtCreator without root privileges;
3) Try to update Qt Creator to newest version (eg. 4.9).

What happens?
Installer downloads the package but complains that there is lack of space on the disc to unpack it.

What should happen?
In my opinion, installer should detect somehow that root privileges are required and asks for root password.
Or at least the error message should be appropriate.