Windows will happily IPv6 address with static, dhcp, and SLAAC at the same time (not to mention all of the transition techs).  To control this behavior, there are two netsh commands for managing SLAAC and DHCPv6 addressing.

The first will disable SLAAC addressing and the second will disable DHCPv6 addressing. Important side note, “routerdiscovery=disabled” disables learning the gateway for DHCPv6 addressing too.  You have to routerdiscovery enabled for DHCPv6 to function.

Substitute “ethernet” for the actual name of your interface.

netsh interface ipv6 set interface "ethernet" routerdiscovery=disabled
netsh interface ipv6 set interface "ethernet" managedaddress=disabled

Bonus tip:  These commands will disable the IPv6 Transition Technologies that are enabled by default.

netsh interface ipv6 set teredo disabled
netsh interface ipv6 isatap set state disabled
netsh interface ipv6 6to4 set state disabled