Yes, that is very odd. I'm trying to figure out which lever controls which brake. That extra lever is for one of the rear brakes, and is on the left bar. Is the other level on the left bar for the other rear brake, or for the front brake? In the former case, the left hand would choose between one of the rear brakes and the right hand would operate the front brake -- one hand for the front and one for the rear, like usual. In the latter case, the right hand would operate the other rear brake, so both hands could be operating rear brakes, and no front brake. Very unusual. I suspect it is the former arrangement.
The only reason that I can think of is for wet weather, when the disc brake may work better than the rim brake. But then why not just have a disc brake on the rear?
I'm curious what problem this arrangement was intended to fix, and whether it actually fixed it.
- DaveS