When adding multiple entity references of the same type but with different values, the contents of them all are collected and applied to each one.
See entityreference_dragdrop/src/Plugin/Field/FieldWidget/EntityReferenceDragDropWidget.php line 142
$entity_id = $items->getEntity()->id() ?: '0';
In my use case an entity reference field on a content type references paragraphs of multiple types. When adding new paragraphs the entity id will not exist so each list will have an “id” of 0. This is used as a key to set the selected items for the list component. Since both lists will have the same type and id of 0 each list will then “share” the items selected.
Needs review
2.1
Code
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
Random value is not an option because there is a chance rand can generate same values.
Adding needs reroll tag. I will create a patch that will address sergei_brill's concern.
Re-rolled with 2.x.
To generated a random number, I combined current timestamp (time()) with a random number (rand()), further reducing the likelihood of duplicates.