Submitting form inside Landing Page from Page Builder preview results in doubled submissions.

Prereq.: Use symfony env DEV.

Steps:

1. Create new Landing Page.
2. Add Form block.
3. Add new form using COTF (e.g. singe line, multi line and button).
4. Submit.
5. Publish.
6. Add a submission from Page Builder preview.
7. Go to Forms / form from step 3 / Submissions.

Actual result: Submission is doubled.
Expected result: Each submission is stored once.

Remarks: Does not affect symfony env PROD. Does not affect submitting from frontend (both from LP and directly from form).