I've set the application launcher shortcut to ctrl+k, but I noticed that under KDE 4.4 I was able to use both to bring up the menu and to close it. Now I'm only able to bring it up. Any reason behind this?

I've also noticed that 4.6 doesn't respond to some of the shortcuts I try to input, such as Alt+B for Quick Access.

On KDE Trunk, Setting any arbitrary shortcut (Including Alt + K) for the menu will both bring it up and close it as expected.