buildah from seems to mount a tmpfs working directory. On success, this is unmounted. On failure, it is left behind on the system:

# mkdir -p /tmp/aaa/root
# buildah --root /tmp/aaa/root --storage-driver overlay from --pull=false alpine
[ lots of errors, expected ]

# mount|grep aaa
tmpfs on /tmp/aaa/root/overlay type tmpfs (rw,nosuid,nodev,seclabel)   <<< not expected

This causes failures on gating tests when STORAGE_DRIVER=overlay because the temporary working directories cannot be cleaned up.

buildah-1.11.4-2.fc30.x86_64 and buildah-1.11.4-2.module+el8.2.0+4595+e1e23178.x86_64