Thanks to Flloyd Kennedy for drawing attention to this Australian cabaret turn, in which Andrew Hansen pokes fun at the way Julia Gillard, the Australian PM, pronounces the word negotiate.
Where most people say nɪˈɡəʊʃieɪt, Ms Gillard says nɪˈɡəʊsieɪt (or with Australian vowels more precisely nəˈɡʌʊsiʌɪt).
In LPD I give both possibilities, prioritizing ʃ. EPD, ODP and the OED do the same. The Oxford Concise gives only ʃ. I think we would probably all agree that the s form has overtones of exaggerated formality, perhaps prissiness. In some cases I suspect it may also be a spelling pronunciation.
For the other words mentioned by Andrew Hansen, in LPD I prioritize ʃ in every case, giving the s variant for appreciate and substantiate, but not for propitiate, initiate or differentiate.
Everyone has ʃ in ocean, never s; but in oceanic some do have s. Most people have ʃ in the middle of species ˈspiːʃiːz, but in speciation -si- is perhaps commoner than -ʃi-. So stress has something to do with it.
(And by the way why does pronunciation have -si- rather than -ʃi-?).
I’m not sure that I can unravel all the historic and synchronic factors involved here.