Utf8 error in abstract

Hi,

in one of our abstracts (OJS 2.4.8) an UFT8 error occured, although we set

client_charset = utf-8
connection_charset = utf8
database_charset = utf8

In nodepad++, the error looks like that

utf8error
Any idea how this could happen?

Deleting and retyping the part of the abstract where it occured solved the problem, but I would like to know if this could happen again. When exporting the (meta)data, the importing script throws an error.

best,
Carola