For some reason, I thought you were refering to the "Quck Selection List" control.
I have tested this just now and it looks like the "Quick Selection Tree" control is not updated properly. Unfortunately I can not say for sure why this is happening.
I have forwarded this to our development team and hopefully this will be fixed in a future version of Advanced Installer.
In the meantime, you could use the "Quick Selection List" control, which is very similar to the tree control.