Partition label is obtained using either:

$ /lib/udev/vol_id -l ${devname}

or:

$ blkid -o udev "${devname}"

depending on whether udev provides or not vol_id. No test against maximum filesystem label length is performed. Lower/upper case does not seem to be taken into account neither.

Persistence set using files to store data works, but doesn't using a partition. I remember to have it work in the very fist tests I made. Probably the long label of the partition (live-rw-doudoulinux) causes this problem. But since the label is used for both file and partition storage, it cannot be easily changed without loosing self-explainability of file names.

The best is certainely to first have a look at the initramfs scripts in order to understand how partitions are found for persistence. Maybe this script could/does cut the long label in a shorter/acceptable one. If this is possible/the case, persistence-gui would then have to truncate the label it computes.

In the worst case, this first DoudouLinux Release could simply not allow persistence in partitions.