IPv6 multipath static routes with different weights and BFD supervision

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Hi BIRD experts,
I face some problems on static routes on IPv6. I try to configure multipath static routes that are supervised with BFD. I use the following conf:
route <DEST_IPv6> multipath
        via <NEXT_HOP1_IPv6> weight 10 bfd
        via <NEXT_HOP2_IPv6> weight 20 bfd;
This does not seem to have the expected behavior since I notice that the static routes are configured with the same priority rather than having the less weighted one with higher priority than the more weighted.
When I try to check the routes passed to the kernel I notice this:
<DEST_IPv6> via <NEXT_HOP1_IPv6> dev eth3  proto bird  metric 1024
<DEST_IPv6> via <NEXT_HOP2_IPv6> dev eth5  proto bird  metric 1024
The same configuration for IPv4 works as expected...
could you, please, give me some initial orientation regarding the issue?

 The BIRD version is BIRD 1.6.3 on Debian GNU/Linux 8 (jessie)



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