Could be. I'm no expert on car electrics but have had your issue before in an Omega I drove years ago. I did the same and just plugged it into the car loom without iso and had the same problem. I'd say that you have no permanent live feed so the headunit memory is wiped every time you switch the ignition off, so it does a full set up each time you start the car. I'm assuming all preset stations and sound settings are lost too?
If the above is the case, and everything else is working fine I'd say permanent live feed issue. Identify the permanent live for the car and unit and check if there is a mismatch between it's position on both connectors. If there is then an iso lead would likely sort it, but they seem to be difficult to get hold of for a mini. I Other options would be to unpick the live feed out of one of the connectors, can be done with a paper clip or a bought tool, and put it back in the right place so both connectors match.
