Shorewall[6] could use an update to the latest, 5.0.14.1 due to a number of bugs being fixed.

Specifically for a given IPv6 configuration:

ERROR: Only one 'balance' provider is allowed with IPv6

The explanation from upstream is:

... solved by upgrading to 5.0.14[.1]. The early IPv6 kernel
implementation of IPv6 did not support multi-nexthop routes so
Shorewall6 didn't either. Now that the kernel supports such routes,
that support has been added to Shorewall6.

I've rolled my own here locally and confirm that upgrading does solve the problem.  A diff of the specfile is pretty simple:

--- shorewall-5.0.8.2-1.spec	2016-05-03 03:53:29.000000000 -0400
+++ shorewall.spec	2016-11-08 22:06:36.661572264 -0500
@@ -1,11 +1,11 @@
-%global mainver 5.0.8
+%global mainver 5.0.14
 %global baseurl http://www.shorewall.net/pub/shorewall/5.0/shorewall-%{mainver}/
 
 # A very helpful document for packaging Shorewall is "Anatomy of Shorewall 4.0"
 # which is found at http://www.shorewall.net/Anatomy.html
 
 Name:           shorewall
-Version:        %{mainver}.2
+Version:        %{mainver}.1
 Release:        1%{?dist}
 Summary:        An iptables front end for firewall configuration
 Group:          Applications/System
@@ -240,7 +240,7 @@
 %{_datadir}/shorewall/deprecated/
 %{_datadir}/shorewall/helpers
 %{_datadir}/shorewall/lib.cli-std
-%{_datadir}/shorewall/lib.core
+%{_datadir}/shorewall/lib.runtime
 %{_datadir}/shorewall/macro.*
 %{_datadir}/shorewall/modules*
 %{_datadir}/shorewall/prog.*
@@ -333,6 +333,9 @@
 
 
 %changelog
+* Tue Nov 08 2016 Brian J. Murrell <brian.ca> - 5.0.14.1-1
+- Update to 5.0.14
+
 * Tue May 03 2016 Michele Baldessari <michele> - 5.0.8.2-1
 - Update to 5.0.8.2