We seem to have a hidden regression introduced via EZP-31287 (ezsystems/ezpublish-kernel#3023). Prior that change when \Ibexa\Contracts\Core\FieldType\Indexable::getIndexData returned more than one Field of FullText type, they were concatenated into one full text value.

This has low priority because it seems no one has found it as, most likely, instead of returning multiple full text value fields, both our own and custom implementations return one FullText field value, where value is an array (it's of mixed type - assumed string|string[]). Fixing this would open the possibility to make the search SPI Field object less ambiguous in the future, by specifying \Ibexa\Contracts\Core\Search\Field::$value as a strict string, expecting getIndexData to always return multiple instances of FullText Field. Other search engines seem to support multiple FullText Fields already.

Steps to reproduce

1. Prepare a clean OSS instance
2. Create either a custom field type with Indexable implementation returning more than one FullText field or add such custom FullText field to one of the existing field type Indexable implementations (please contact the reporter if you need help).
3. Reindex (via ibexa:reindex command) search data
4. Try to search either for second or first FullText value (only the first one found is indexed, but which one depends on DBMS).

Actual result

Observe that the results are not found for one of the phrases.

Expected result

All indexed data via FullText fields can be found with LSE