Is glottalisation where [t] is replaced by a glottal stop, like is common in Cockney? Australian English is much less varied than American or British, but still varied enough that I can believe that, even though as far as I'm aware it doesn't feature in my accent.

perhaps [i] (and potentially other vowels) block flapping for you.

Yeah I suspect that's probably it. I recall seeing a list of vowels where it's done in Australian English, and I think [ɪ] was on it, but not [i].