According to the support of my hosting this is a known bug in the actual version of phpMyAdmin.
He recommends, to have phpMyAdmin or alternatively MySQLDumper installed on the server directly to run without plesk.
I found an addional work around:
If a make an DB Export in phpMyAdmin/plesk without checking the send buttom, I get a sql dump on the screen which ist correct, without those messed up link statements.
Mark the whole dump, ctrl-C - open a local texteditor and ctrl-V the whole sql stuff into a text document. Save it locally and you have a correct sql dump. Import it to a new database, login to the modx manager, adjust the pathsettings in the configuration and everything works. Well it worked in my case at least!
Only remaining problem if you work on a local windows machine: notepad cannot handle the utf8 character set, so all german Umlaut (ä,ö...), french accents (é..) and other language specific signs are gone. I guess, this is easly solved by using an editor, which can handle utf8.
I hope this helps others who are bothered by the same bug.
Works perfectly. Thanks Sharkbait!
