Comment 1 for bug 1489855

Did you ever resolve this?

I think I have the same issue with the final release of Ubuntu 15.10
ece816e12f97018fa3d4974b5fd27337 *ubuntu-15.10-desktop-amd64.iso

Here's what I've done so far, I've combined concepts of different guides. I'm starting from a Windows 10 environment.
1) I used diskpart on the windows command line to wipe the partition table off the usb drive, As window's "Disk Management" can be restrictive (next step). Any good partition tool would do.
2) Created a 1.2 GB fat32 partition, 4096 cluster size. The rest of the usb is left unpartitioned. I determined the size by trial and error, originally I used a guide that suggest installing on the whole usb and resizing/shrinking, I found this to be easier.
3) Used the tool at pendrive linux. Added about 70mb of persistence.

Until this point everything works as expected. It Boots to the live environment, it has persistence and I'm using only a portion of the USB.

4) I created two ext4 partitions. My USB drive is 16GB, and wanted to have more control of what would be in and out of casper-rw So the first one is labeled "casper-rw" and the second one is labeled "data".

At this point I can reboot, and everything is just like before, the system will continue to use the casper FILE, and not take advantage of the PARTITION. Both partitions are automatically mounted on /media/ubuntu

It's when I delete the casper-rw file that the problem happens. After a few failed attempts, I decided to move it out instead. I'm using windows for this, and it sits on my desktop while I test. I can then revert successfully.

Summary:
When I boot without the casper-rw FILE, I get a busybox, even though I have the casper-rw PARTITION created.

I expect it to automatically revert to using the partition.