I doublechecked it again. Made several full scans and looked especially, in addition, in the folders which could have something to do with Ocpn, without success. The mystical is that I still can select these icons but don't find them on the harddisk. I also checked the icons of S57 charts
but theses are also different. So I have no more idea where and how
I could find the evil icon - but I will not use it anymore. Will see when I upgrade in some time to a new Lubuntu with the then current
Ocpn whether these are still there or not.
Thank you to all again that my system is stable again,