iTunes doesn't allow me to create playlists and playlist folders anymore

I'm a bit stumped. So I was trying to add some MP3s to my iPhone 5 using iTunes and it simply doesn't react to the clicks on the respective symbols anymore.

Here's a partial screenshot:

The shown playlists and playlist folders are contained in a parent playlist folder, which was selected prior to attempting to add a playlist.

The two controls at the bottom with the plus and the cog don't work. It's as if they're disabled, but it's hard to tell for me in this Apple-style GUI.

Does anyone have an idea how I could convince iTunes to let me create (smart) playlists and playlist folders again?

NB: this is the music "tab" and I have opened the "Device" node for my iPhone on the left hand side and selected the parent playlist folder there.