Files whose names begin with a dot (".foo") do not get distributed among the subvolumes. All of them end up on the same subvolume.

This happens with any distribute setup. My test environment is:

4-subvolume distribute over storage/posix

# cd /mnt
# mkdir dot nodot

# cd nodot
# for i in {1..64}; do touch file.$i; done

This created files on the four subvolumes:

subvol 1: 19
subvol 2: 14
subvol 3: 14
subvol 4: 17

# cd dot
# for i in {1..64}; do touch .file.$i; done

subvol 1: 64
subvol 2: 0
subvol 3: 0
subvol 4: 0

This is 100% reproducible. min-free-disk is not a factor. There is ample disk space available, and all four subvolumes reside on the same disk.