Inline Entity Form won't submit after form error

PHP doesn't have operator overloading, so whatever the problem is exactly, it has nothing to do with that.

We need steps to reproduce. Closing until we get more information.

Reopening, I'll try to reproduce. I think by "exists" he means "selected"

I was able to recreate the error, after making a change to the function entity_browser_entity_form_reference_form_validate

-        if ($value['entity'] == $attach_entity) {
+        if ($value['entity']->getEntityTypeId() == $attach_entity->getEntityTypeId() && $value['entity']->id() == $attach_entity->id()) {

I think that's not working now. I created an issue for that:
#3044316: entity_browser_entity_form_reference_form_validate fails to validate

I have seen this error before, now that I think about it.

Here's a video of the error. It seems no action can remove the form error once it's been set.

$form_state->getValue(['field_test_content', 'form', 'entity_browser', 'entity_ids']) = 'node:5 node:5 node:5 node:4 node:4'

even though I only have one item previously selected, and I'm selecting one item.

Here's a fix for this and #3044316: entity_browser_entity_form_reference_form_validate fails to validate

Test only patch should fail.
Patch with test coverage should pass.

Adding minor coding standard fix.

Here's a different "test only" patch, as the first one is demonstrating #3044316: entity_browser_entity_form_reference_form_validate fails to validate, rather than this issue.

Same as #15, just reposting after posting #17, so last post is good patch.

Went ahead and committed. Berdir writes "had a quick look, seems fine, ajax id stuff is always tricky".