That would be the aforementioned "P(x) > 1.0 bug".
I got that bug once, with a Samurai, in the final vanilla patch (1.6, was it?), so I don't think they quite squashed it, even by then.
I haven't gotten it yet in 2.08, despite several attempts to flush it out with Samurai and Cho Ko Nu.
I really, really hope there aren't any more of those display bugs left. The game is buggy enough, as is, without the odds being displayed incorrectly. I hate when the game stops displaying tool tips (or balloon help/balloon text/popup text, as I've seen it referred to, in some forums). When is Firaxis going to fix this bug?