bogus error in overlayfs mount

[josepmaria79]

For some reason, when mounting multiple lowerdirs I get this error:

wrong fs type, bad option, bad superblock on overlay, missing codepage or helper program, or other error.
dmesg(1) may have more information after failed mount system call.

What is interesting is that the command works with 9 items but not with 10.

This is the command I use:
mount -t overlay overlay -o lowerdir=/dir1:/dir2:/dir3:/dir4:dir5:/dir6:/dir7:/dir8:/dir9 /merge-mount-point

This works fine, but if I add :/dir10 it fails with the error above. And nothing is wrong with the file system on /dir10, because I can interchange it with /dir9 and it works. That is: ... :/dir8:/dir10 ... and no problem there.

So is there a limit somewhere in overlayfs? It didn't happen last month... maybe related to a recent kernel upgrade or util-linux package? I tried to roll back to packages from 3 months ago and error is still there.

Any other hint of a possible culprit package?