If grub-install fails, ubiquity screws up in two ways:
1) It unmounts /target/dev, so when you select another location ( the correct one ) to install grub to, that attempt fails as well
2) After selecting a different loation, the installer goes immediately to the installation complete dialog, while attempting to install grub in the background. At this point, clicking just about anything causes ubiquity to crash.
You can easily reproduce this in a vm with two disk drives. Install the system on sda, but select sdb1 for grub. This will fail because cross disk installs require the embed area. When the prompt comes up to pick another location, pick sdb or sda, both of which will work if you chose them the first time. The installation complete message pops up immediately. A second or two later, the grub install failed dialog comes back. In syslog you will see the second attempt failed because grub-probe could not find /boot. This is because /dev is not mounted in /target at this point.
We get many crash reports filed to grub as a result of this where the wrong grub target was chosen the first time, then the user picks the correct place, but installing there fails too.
Further, often the grub install failed dialog box locks up and won't respond to any button presses.
Still there in Lubuntu 16.10 32-bit. I'm installing using a bog standard quad-core desktop, from DVD, but onto 40 GB IBM Thinkpad PATA harddisk (using a laptop-to-desktop PATA conversion cable. No other operating systems, no RAID, no encryption, etc. Using the default "Use Whole disk" in the installer. (The number of reports is small over many years, but maybe not everyone bothers to create an account.)