Interesting, I would have expected a little more action from the 0.5u. Could be right what others are saying that it's some bounce from the steeper drop & lower #s yesterday. I probably would have gone with 0.6 today, but after reading the thread, 0.5 makes sense to me as well.
The thing that stands out to me is that yesterday's pattern was not a nice U-curve to a "normal" nadir (+4 to +9 say), so unless you have a cat who typically nadirs late (which I don't see from earlier data, there is often a much earlier nadir), *something* is up. There are several possible explanations, but to me the first line of approach (regardless of the explanation for the curve) is to lower the dose a hair and see what happens. If the 88 had come at a +6 and you had something like a 60% drop from PS to nadir, then I'd be saying the dose was perfect. When the pattern doesn't match that (barring a cat with a history of a different pattern), then I start to question the dose.
Don't tear your hair out though, I don't think 0.75 is unsafe or anything like that, at least not on this kind of PS. If it isn't making sense to you and you are still having dreams of shooting 1u though, let us know exactly what part isn't making sense.