Odd but possibly explicable phenomenon on the motherboard: my case's front panel is connected to a USB header that doesn't seem to work now that I've stuck a wifi/bluetooth card into one of the M.2 ports.
I say explicable because the previous PCIe wifi and bluetooth card I'd been using required a USB header to use bluetooth, and since I only had the same one for the front panel, I didn't connect it, favoring the front USB2 port over bluetooth in that moment. My suspicion is that both of those connectors are somehow handled over the same PCIe lanes, because I didn't touch the header at all and the port should have continued working otherwise.
This isn't a big issue, even if it means that I've just wound up in the exact circumstances I was trying to avoid. I have plenty of rear ports and spare (UBS3!) hubs, and certainly if I needed to could install a PCIe-based USB header in another slot. Mostly it's just funny/frustrating, especially since the user manual doesn't suggest this is even a possibility.