Package: debian-installer Version: 20150422 Sadly, I can't report this from the machine where this occured, but the setting is simple: new net-install on a machine with one SSD (sda) and three HDs (sdb,c,d). Trying to setup a maintenance partition before completing final setup & install, so it's a little odd. The SSD plays no role at all in this other than to hold the sda position. All three HDs partitioned with small sdX1, sdX2, not used in this install. All but 10G of remaining disk is assigned to the extended partition container, and that last bit becomes sdX4. Setup RAID 10 on sdX4's, install, all is fine until grub setup, which fails with a cryptic message about "/dev/md".
Cutting past headscratching, found that same result for RAID 1 as well, and ditto for RAID 1 on sdX1 (with no other HD partitions). Eventually I made one last try and manually entered the grub target device (hey, it wasn't obvious to me - I'd *been* asking it to iunstall on /dev/sdb in the menu all along, right?). When I enter /dev/sdb, hey, it works! I'm not sure what package provides the dialogs that collect this info and invoke grub-install, but they seem to be getting confused and pass the nonsensical "/dev/md" when I choose /dev/sdb. Installer is net booted from September netinst image, everything else is as it came from the repos this afternoon. 64-bit kernel, pretty minimal install (only standard utilities selected from taskmanager).