After using gnome-tweak-tool on my 15.04 with Unity the keyboard layout switch (Ctrl L+Shift) doesn't work as before.
Now I always have to complete the exact sequence: press Shift first and hold it, then press Ctrl L.
Simultaneous Ctrl_L+Shift doesn't work anymore and I don't know how to get it back.
Even custom setting of layout switch to "Ctrl L+Shift" doesn't help.
Enabling Show location of pointer at Mouse section of gnome-tweak-tool changing the Ctrl+Shift behavior to that I described in my question.
Disabling this feature restores normal behavior for this shortcut.