Renward Brandstetter, An Introduction to Indonesian Linguistics…
“ Many of the formatives that serve to make word-bases may also perform other functions in the economy of language. Thus in several languages the above-named prefix ka- forms the passive. [57] Thereby it may happen that one and the same root carries two ka-'s, the one forming the word-base and the other the passive. So from the root sut, which occurs, e.g., in Old Jav. kusut, “to move oneself to and fro”, there is also formed an Old Jav. kasut, “to shake”, and the passive thereto is kakasut. — But most of the formatives that serve to make word-bases are, in fact, confined to that function ”
