I was just looking around my config on an RB1100AHx2, which has seemed to be working fine for a while and I noticed that all of the ethernet interfaces had "speed=100Mbps" (/interface ethernet print detail)
This wasn't a config that I set ... and an "export" didn't show the setting, which leads me to believe that it's the default.
This conflicts with the manual that says "By default, this value is the maximal data rate supported by the interface".
I seem to be able to change it to "1Gbps" from the command line and things still work ok.
I haven't checked what speed it's actually negotiating yet - my internet line is 100meg, so I probably wouldn't have noticed anyway, but either way this is a bug isn't it?