i never heard of a similar lockup but still could be a partial update, verify in synaptic that you have all the packages form task.kde4 and task-kde4 minimal and extras installed, if possible verify another repo, disable the one you have and enable another
how many users do you have, only user and root? does this happen as root?
if only happens as your user, you could rename the .kde4 folder inside your home folder, some config could fail and give you this result, after the rename of this folder kde4 will generate another empty config folder