Experimented with 6.47 (upgraded from 6.46.6) on a Mikrotik CCR1072, after the upgrade the 6-to-4 tunnels stopped working.
TX on both sides but no RX... The "Tx/Rx Drops" counter increases (but is lower than the "Tx/Rx Packet" value, although the is no traffic coming trough).
The other end (the concentrator) of the tunnel is a CCR running 6.45.3 not yet verified what happens is both sides run 6.47.
Also not yet verified if the limited MTU (although this worked fine with previous routeros versions) is related.
The 6-to-4 tunnels run over a PPPoE connection, the PPPoE concentration is not done by the Mikrotiks, it done by a Juniper MX.
After downgrading the packages to 6.46.6 everything works fine again (RouterBOARD / Firmware still running 6.47).