I have noticed that among the several words that have the termination -ciate (or derivatives of these) sometimes the pronunciation of the 'c' is /ʃ/ and sometimes /s/. That is, sometimes palatalization occurs (as in "attention" or "commission") but some other times it doesn't. For example:
/ʃ/: Emaciated, excruciating, officiate.
/s/: Pronunciation, enunciate, glaciated.
(according to the dictionaries I checked)
Is this arbitrary? Is there any pattern/rationale behind when it is one or the other? Or in other words, can one predict if palatalization occurs by looking at the part of the word preceding -ciate?