I've experienced this on OpenWrt as well. There's a backup/restore config files button but it's sort of a best-effort type of operation. If you are restoring across many versions and the config files are no longer sane, you will end up with a broken system. But the config files were restored exactly as advertised :)
Thankfully all the config files are plain text and can be manipulated however you like. It is usually not too difficult to take working config while fixing or disusing problematic files.
At least on the hardware I've owned, OpenWRT has to be reconfigured after version upgrade or else it becomes unstable.