Looked into it and I see that the device indeed shows up, I just can't mount it. I run Linux btw.
I'll PM the device details so you can investigate. One thing I noted was that it shows up with a different device subclass than what I get when i use the USB connection feature in the XMB.
Edit: subclass 6 is SCSI and subclass 5 is obsolete according to docs.
Edit 2: Lol, can't use attachments in PMs. Ok, attaching here instead. psp-usb2.txt is when mounting with XMB, psp-usb.txt is when mounting with your tool.