About 9 Years ago, FreeBSD has introduced a functionality in sysinstall(8)’s partition editor, which is to mark a partition “active”.
However, unfortunatelly, the implementation contained a flow from the day 0 it was introduced. Sysinstall(8) depends on user’s sanity not to mark only one partition as active on one disk.
This turned out to a potential damage of disk partition table. With two partitions marked “ACTIVE”, you will get the following message:
“Invalid partition table.”
Then system will halt.
Resolution: While I believe that it’s user’s responsibility to know marking two active partition tables will render a unbootable system, I think it might be good to have a sysinstall(8) function that eliminate the possibility of having a user shoot his/her feet, as discussed here.