Prophet 6 Custom Patches dissapearing

[Hale]

Hey guys,

I recently bought a Prophet-6.

I'm extremely happy with the instrument, but I have one slightly annoying issue.

I bought a soundbank on the internet (Luftrum). I put these patches on my prophet through MIDI-OX, following the official guidelines and the ones supplied by Luftrum.
However, when I turn my prophet off and on again, the slots these patches were in get reset back to the factory ones.
This also happens when I calibrate the P6,

The patches install on slots 100 to 199.

Am I doing something wrong or could this be a defect?

Thanks in advance!