[diskless mode] lbu ignoring whole directory instead of one file

When using lbu on diskless installation to ignore etc/zfs/zpool.cache config file in /etc/zfs, the whole folder is ignored.

Steps to reproduce :

Create a bootable disk with setup-bootable from Alpine 3.15.0 x86_64 Extended ISO
Boot from it
Install zfs : apk add zfs
Import existing tank : zfs import tank
Exclude cache file : lbu exclude /etc/zfs/zpool.cache
The whole /etc/zfs directory is now ignored

Thanks