What you should do is enable I/o debug mode before going into the changer control and pressing the scan button.
From what I recall, all it's doing is loading the disc from slot X, waiting a while for it to become ready, unloading again and preceding to test the next one.
It looks to me as if those commands are getting stuck on your system for some reason.
The debug enabled log file may shed more light.
Enable I/o debug mode by pressing F8 or by going into the settings and enabling it on the I/o tab.