Can't find target JOOL_SIIT when iptables for both ipv4 and ipv6 are used

[bvlarsen]

Similar issue has been raised before, but this can not be worked around by running v6 before v4, as for instance with target MARK. The target is JOOL_SIIT

OS: Ubuntu 20.04 with kernel 5.4.0-104-generic
Python3: 3.8.10
Python3-iptables/focal,now 0.14.0~ds-1ubuntu4 amd64
JOOL_SIIT: jool-dkms/focal,now 4.0.7-1 all

code:
table6 = iptc.Table6(iptc.Table.MANGLE)
table6.autocommit = True
chain6 = iptc.Chain(table6, "PREROUTING")
rule6 = iptc.Rule6()
rule6.target = iptc.Target(rule6, "JOOL_SIIT")
rule6.target.instance = "inst100"
chain6.insert_rule(rule6)

table4 = iptc.Table(iptc.Table.MANGLE)
table4.autocommit = True
chain4 = iptc.Chain(table4, "PREROUTING")
rule4 = iptc.Rule()
rule4.target = iptc.Target(rule4, "JOOL_SIIT")
rule4.target.instance = "inst100"
chain4.insert_rule(rule4)

[hunbalazs]

This is libxtables related, the same issue happens with any multi protocol target (for example TPROXY)