[...] despite being quite sure that I'd specified that the system clock was set to UTC, when I brought the system up, the date command reported the time as the UTC time, but with the correct timezone (EST; I had specified the timezone as America/New_York during the install). I redid the install to be absolutely sure I specified that the clock was set to UTC and also checked the system time in the BIOS. The system clock is indeed set to UTC and I set the localtime vs UTC choice correctly during installation. The system is not making the timezone adjustment.This is because, despite what I said to the installer, the ClockMode variable in /System/Settings/BootOptions is set to LocalTime.
[...] in the first install, I specified that the hardware clock was set to GMT and specified America/New_York as the timezone. In the installed system, the date command gave me GMT time, with a an EST timezone designation. The timezone correction isn't happening. Suspicious that you might have the sense of a test reversed (Dragonfly BSD had a bug like that some years ago), in the second install, I specified that the clock was set to localtime, timezone America/New_York. The time is still displayed as GMT/UTC, timezone EST. This is actually correct in this case, since no timezone correction is needed if the system is told the clock is set to local time. But it disproves my backwards-test theory. The bug is that when it is told the clock is GMT/UTC, it fails to do the timezone correction.
As reported by Don Allen on gobolinux-users: