Got the exact same problem on a Routerboard 1100AHx4. Afaik thats the same Hardware as the RB4011 (minus the sfp+ port).
Edit: I noticed this Issue on 7.9. Upgrading to 7.9.3 did not help. Downgrading to 7.7 seems to fix it.
Edit2: seems to be fixed in 7.10rc3