System: (K)Ubuntu with KDE 64 bit, German
Usually one enters a "protected space" by hitting these keys: Crtl+Shift+Space. Until version 188.8.131.52 this worked (I installed a Kubuntu from DVD to a VM to test it.)
At least since version 184.108.40.206 and all later ones I installed from the Ubuntu-repository at http://ppa.launchpad.net/libreoffice/ppa/ubuntu for trusty / 14.04 it is not possible to enter the "protected space" this way. It still works to insert a "protected space" by the menu. (Translating back from German it's probably menu insert -> formatting sings -> protected space.)
This behavior can be reproduced on a completely new user account in Kubuntu 14.04 64 bit. It's not evil, but it's annoying.
I hope I didn't submit a bug that's already known (didn't find hints on google or bugzilla) or a very special problem of my computers.
Hi! Today I found the solution. When only pressing control and space, now (probably since an update) a small window appeared showing the change of the keyboard settings - even though I only activated one layout! With this information the solution was easy to find: a ubuntu program called "ibus" took over this shortcut globally and there is no (or at least no easy) way to change it. I didn't need ibus, removed it and after a restart, control+space was not pre-used anymore => control+shift+space works again!