It seems that some feeds I subscribed are being replaced by random other feeds that I did not subscribe to. For example, in my “economics” folder, I was subscribed to "http://www.telegraph.co.uk/finance/co…. It seems that this feed has been replaced with "http://www.telegraph.co.uk/technology…. It is possible that this mix-up already happened during the import from Google Reader, I’m not sure.
When adding the first feed manually, I end up with the second one again. It looks like this problem is not related to the Google Reader import.