The typewriter story. may not be a figment of your imagination, but doesnt it shriek at you that it's a figment of
somebody's?
As I ply my trade in Theoretical and General Linguistics, and unlike so many such tradesmen, actually know a lot of languages, my polyglot instinct at once told me that this is bound to be a matter of contextually determined
allophony, in which the realizations (roughly, pronunciations) of a phoneme are determined by the proximity of another. Native speakers are quite often not aware that this happens, and unable by mere volition to make the difference out of context or not infrequently even hear it.
This is particularly likely to happen with /t /and /i / in all sorts of languages, and typically the /t/ is then realized more or less like English 'ts' or 'ch' , or as in this case, 's'.
http://en.wikipedia.org/wiki/Gilbertese_langua ge is right there for us to confirm that this is indeed the case with Kiribati. It says "/t/ is lenited to [s] before /i/", and has a linked explanation for 'lenited', but you don't really need to bother with that, as it's more or less what I have written above.
What is so delightful (and typical) about this is that it is claimed that the pronunciation with s was intended from the start to approximate to the pronunciation of 'Gilberts', since it is the nearest the speakers of the language can get to it.
Perhaps more familair examples of this sort of thing would be Japanese "Meri-Kurisumasu" or Hawaiian "Mele Kalikimaka," for Merry Christmas.