1. Open item edit form and add a script type preprocessing step.
2. In the value using multiline edit add two empty lines and a symbol.
3. Open preprocessing test popup form.
4. Inspect the hidden textarea element and see that there is only one new line left instead of two.

After ZBXNEXT-3970 (ZBXNEXT-5409) is live, this will also affect preprocessing type "CSV to JSON". The first two parameters can be empty. So the preprocessing parameters can hold "\n\n1". And in preprocessing test popup form after jQuery.append is performed to display the form, it will be converted to "\n1" for reasons unknown. Same as it would be a script type. A temporary solution in popup.preproctestedit.view.php. was created to fix only for preprocessing type "CSV to JSON", but a better solution is required.