pdb-before_validate_field executed also when updated entry

Wordpress version: 4.9.5
PDB version: 1.7.8.5
PHP version: 7.1
I managed to install a plugin to implement the pdb-before_validate_field function. I want to create custom messages when the email field in my entry is duplicate. This works fine when the data is initially entered. But when the user uses the [pdb_record] link and edits his entry, the check is applied again and fails, because indeed this email is already present. Is there a solution to this dilemma?