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I noticed this a few weeks ago on live, but when Tristana last hits a tower, the tower explodes from her E's passive. While very minor in terms of gameplay, this doesn't seem to be the intended use of the proc. I tried it a few times in custom games and it looks like its easily reproducible.
I would also assume other buildings proc the passive as well, but there are so many situations where this is both hard to accomplish in a regular game and completely useless to do that it was probably left unnoticed .