I created a software RAID 1 system a few releases ago (around 9.x I believe) over 2 identical disks. 3 partitions on each disks that up to 12.2 were recognized as md0, md1, md2. They stayed that way through a fresh install of 10.x, 11.1, and 12.1. (I install the system on another disk, so I never had a need to touch the 2 disks hosting the RAID before)
With 12.2, they showed up as md0, md3, md125, and md127 in the partitioner. Not a big deal for me since these were Reiser file systems that I wanted to reformat anyway. But there is obviously some sort of issue with the partitioner.