If I copy a file from the source-tab to the destination-tab, the modification-timestamp should be kept but the creation-timestamp should be set to the current system time.
I think this is the most expected behaviour that reflects the actual operation, but unfortunately the 'timestamp preserve' option overrides the creation-timestamp anyway.
How I can I solve this?
Thanks in advance for any help!
Go to Settings -> Preferences - Miscellaneous - Advanced and turn on no_copy_creation_time.
I guess it depends on what the creation timestamp means to you. To me it's when the data was created and I find the idea of data that was modified before it was created quite unexpected. 
I also like that I can copy a file, do something to the original, then copy back over the original and have everything the same as it was, without the creation stamp being changed.
I guess doing things the way you suggest would allow you to see when the copy of a file was branched from the original. It's not without its uses but I, at least, find it counter-intuitive, for what that's worth.
Anyway, the good news is that you can have it either way.
I totally missed that advanced options up to now. Thank you very much!
Yes certainly you are right, but I like to think of the creation timestamp as the time when the file was created (not the data inside the file). For the data I would expect some timestamps inside of the file (e.g. the various timestamps of a PDF document stored as meta data).
On the other hand it is the same behaviour that the Windows Explorer and other tools have teached to me in the last years. Thus my expection was formed by Microsoft! 
The advanced options are easy to miss. 
If timestamps are for the file rather than the data then shouldn't the modified time also be bumped after a copy? It seems inconsistent for the modified and created timestamps to be about different things.
I guess there's no point arguing with Explorer, though, and if you're used to that behaviour and take advantage of it then fair enough. You're not the only one since the option was added after someone (many years ago) pointed out the same thing.