"tahoe mkdir" doesn't accept $CAP/path arguments?

[zooko]

I was trying to create a subdirectory of a directory using tahoe mkdir. I ran this command-line:

tahoe mkdir "URI:DIR2:nuiaen5vpvszo2n55ghewatdp4:cu5irq3movjgywuxw6ofviizu25qiz2srglg5voqymiryblkjhmq/Best of Bootie 2009 v.2"

It emitted this output:

URI:DIR2:zr6vjl4s7ltl23p4wojc4xiuoy:njhn5fkb4r5hjv7czuaqn5cbtyu4epnuibksxnwun2zp4y7pazpa

and exited with exit code 0.

But, it did not create a subdirectory:

$ tahoe ls --node-dir=~/.tahoe-testgrid/ URI:DIR2:nuiaen5vpvszo2n55ghewatdp4:cu5irq3movjgywuxw6ofviizu25qiz2srglg5voqymiryblkjhmq | grep Booty

So what did it do?

[zooko]

My guess is that it silently ignored the argument and created a new unlinked dir and returned the cap of it.