Live desktop boots wrong install

[Zoltan The G]

Apologies, this is a strange one and hard to describe...

Kaby Lake i7, 2 SSDs, windows 10 pro 1607 on NVMe SSD. UEFI/GPT all drives.

Ubuntu 16.04.2 _live desktop_ on SATA SSD. By that I mean live "CD" contents copied to a FAT32 partition. I use it that way since I use grub2 to launch other tools in the FAT32 partition in addition to Ubuntu. Acronis, for example.

If I boot _the same_ Ubuntu live version on a flash drive, I get the flash drive's grub menu and select "...try..." what actually boots is the live desktop on the SSD. I can tell since the flash drive shows up as removable and the SSD's partition is mounted as /cdrom.

If I obscure casper on the SSD ( casper->casper_OBSCURED) the flash drive live desktop gets booted fully. A persistence file on the SSD also will get used unless I obscure that.

If the live desktop versions are different, the flash drive desktop gets booted as expected.

I can also avoid the problem by booting a loop-mounted ISO of the live desktop on flash, even if it is the same version.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubiquity-casper 1.376.2
ProcVersionSignature: Ubuntu 4.8.0-36.36~16.04.1-generic 4.8.11
Uname: Linux 4.8.0-36-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.5
Architecture: amd64
CasperVersion: 1.376.2
CurrentDesktop: Unity
Date: Sun Mar 12 16:52:09 2017
LiveMediaBuild: Ubuntu 16.04.2 LTS "Xenial Xerus" - Release amd64 (20170215.2)
PackageArchitecture: all
ProcEnviron:
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: casper
UpgradeStatus: No upgrade log present (probably fresh install)