Just an update: I did a clean install of Kubuntu 5.10 and chose "Pacific" as my time zone. It worked this time. My time zone was set to Pacific. I then successfully changed my time zone to UTC
and then successfully changed it back to Pacific. So, my previous struggle with the stuck UTC setting was either a fluke, or something that I had broke on my end. Since I can no longer
reproduce this problem, I'm going to voluntarily mark it as resolved ("Not A Bug"). Sorry for taking up your time with this.
Just an update: I did a clean install of Kubuntu 5.10 and chose "Pacific" as my time zone. It worked this time. My time zone was set to Pacific. I then successfully changed my time zone to UTC
and then successfully changed it back to Pacific. So, my previous struggle with the stuck UTC setting was either a fluke, or something that I had broke on my end. Since I can no longer
reproduce this problem, I'm going to voluntarily mark it as resolved ("Not A Bug"). Sorry for taking up your time with this.