Machine sits like this, waited 6 hrs ( went to bed ) came back no change.
This machine has 5 OS's on it and can take 5 mins or so to scan all the disks while, for example, doing a grub-update.
No EFI Boot
installing to sdb6 ( as root ) and sdb7 ( as home ), replacing a previous version of Mate 15.10 ( updated from 15.04 Mate ).
Re-Installing so I can get rid of a btrs disk and as a clean 're-pave' for 15.10
From the sound of things, ubiquity (the first boot installer) is having problems on your particular set up. Not sure if it’s a GPT or MBR partition table, if that would make a difference.
Next time, I’d suggest using GParted (from the live session) to create and format your new partitions. Then when using the “Custom” option, choose not to format the partition. Swap would want to format automatically, beware since this will give it a new UUID, in case it’s shared with other Linux OS’s.
Thanks that got it, just needed to look at it from a different direction 
