Hello Beat,
Sorry for the slow reply.
Yes, I understand this is somewhat confusing. It is to me anyway :) The issue is that output is supposed to be escaped so JavaScript or other nastyness doesn’t become part of the page content.
I just did the following:
I removed the text in the settings. I saved those settings. The textarea was filled again with the default text and I saved that. The textarea now had a won't in the text.
I went to the string settings and cut and pasted that same content. Then I saved the string settings.
This resulted in a correct replacement of the string.
Issue was when saving the strings again (for example by adding a new one). Now the string had an escaped text with won\'t. Now the text replacement did not work.
I will look into trying to have both settings act and work the same.