Looks like in recent builds, the reboot command has stopped working, at least it has for me.
I use this command for my nightly router reboot, and I think it's the same as what the reboot functionality in the Luci UI uses, which also is not working for me. The UI just hangs for a little while and reloads the page without having actually rebooted.
The only thing that does work is using
reboot -f, but this causes the router to reboot to the alternative partition.