If you have selected any text in your editor (even without using Ctrl-C or Ctrl-X to put it on the clipboard), then when opening up the Search with Ctrl-F (or clicking the 'Find' button) will have that selected text automatically put in the search field -- you do not have to do anything to put that selected text in the search field (other than select that text in the editor). As a test, you could copy your text to the clipboard, then hit any arrow key before opening the Search field so that no text is selected; then the way you were trying to do it will work.

Nope, that's not an user error... If you want, I can send you a video of my screen, where I first mark a text, copy it, then I press Strg+F, then delete the text in the search field and then i paste the text by 'Strg + Y' and the text is pastet twice in the search-box.

You both must be using one of the later versions of greenfoot. You should probably shoot an email to the greenfoot team about this.

Well, I'm using the latest version... I Downloaded it yesterday under the 'Download'-Tab and then I clicken on the Windows-Button for downloading it for Windows 10... :/ May you could write the Email-Adress here?

The mail address is this: support@greenfoot.org. Found here: About → technical support → https://www.greenfoot.org/support I just wrote a mail about the problem with a link to this discussion.

Thanks for reporting this. I’ve added it to the bugs database: http://bugs.bluej.org/browse/BLUEJ-940