Hello, I also had this problem, the power supply of the radio was wrong, that means you have to take out the radio with the enclosed tool (2 pins) and swap the 2 power cables as described in the manual. Greetings Thomas

What SBigoglys wanted to say was:
You have to swap the "permanent plus 12 volts" with the "ignition plus 12 volts". After that, the memory should remain intact. It is best to measure with a voltmeter beforehand whether the "permanent plus 12 volts" is also retained when the key is removed. If not, lay an extra cable from the battery with a fuse etc....