Target Disk Mode is read-only?

I am connecting a G4 iMac (10.4.11) to a MacBook Air (10.9.3) in Target Disk Mode using a Firewire cable and a Thunderbolt-to-Firewire adapter. The iMac works perfectly by itself. In TDM, it shows up as read-only. The Get Info box says I have read and write permissions, but even after unlocking it won't let me change anything, and above that area it says "You can only read." Why is it doing that, and more importantly (especially since I no longer have a Tiger DVD or any other boot volume for the iMac) how do I change it to read/write?

 

Given that it won't allow me to change anything at all in the Get Info window (and, indeed, both the action button and the +- next to it are grayed out), how would I accomplish that?

 

The G4 works perfectly on its own, including letting me read and write. I'm not sure what to change in there to allow the same with it mounted as a target disk but will experiment next time I'm with that machine. One thing I forgot about: the "ignore ownership on this volume" box is checked and not grayed out, but clicking it brings up a short "cannot complete" type error alert. If I'd had any sense, I'd have paid better attention, but will look up the code (if there was one), also next time I have it.

Thanks. If I still had a working PATA-to-USB adapter, I'd pull the drive out and try it in that... but it *shouldn't* make a difference.