Oh, that's interesting - I'd noticed that in one system earlier, but now that you've mentioned it I see I have at least one more.
I have a population 61,000 system with a (non-controlling) faction that dropped from 25.1 to 12.7, and might have wanted to drop more if it didn't get a pending war; I had hit them yesterday with failed missions amounting to 63+'s. Or minuses, depending on how you look at it.
In a 2 million population system I have a (non-controlling) faction that went from 26.4 to 30, after I made twelve profitable sales, gave them 20 mission +'s, and cashed bounty vouchers in twice. That one's a little murky because someone may be undermining that faction (with a small effort).
Then I have a population 172,000 system whose controlling faction shot from 57.9 to 67.2. I did so little there yesterday that I didn't even note it, but that system gets a fair bit of random traffic and support.