fix: don't submit data of removed fields

src/Form/Service/ParticipantFieldHandlerRegistry.php

@@ -294,7 +294,9 @@ class ParticipantFieldHandlerRegistry
     {
         // Sync fields for all registered handlers
         foreach ($this->handlers as $fieldName => $handler) {
-            if (property_exists($participant, $fieldName)) {
+            // Only sync fields that were in the original submission
+            // This prevents adding extra fields that would cause validation errors
+            if (property_exists($participant, $fieldName) && array_key_exists($fieldName, $participantData)) {
                 $dtoValue = $participant->{$fieldName};
                 $participantData[$fieldName] = $this->convertDtoValueToSubmittedFormat($dtoValue);
             }