About the relation of files and APPs, I am nervous. Therefore, I always change a default setup of QT installer, and am made to remove relation except mov, aiff, and pict.

I at least have experienced this phenomenon in two different machines.
My acquaintance has also experienced the same phenomenon.
It is strange that users with this problem and users without this problem are exist.

I am not going to install QT until the solution of this problem is found.

Thank you all