Older values in post custom field do not appear in filters when the type is changed

Some posts with a populated custom field cannot be found using the custom field filter, while newer posts work as expected.

This seems to affect only older entries.

A likely cause seems that the custom field was initially created as a Text field and later changed to a Number field.

Older values saved in the original format are not indexed or matched by the current numeric filter.

As a workaround, editing an affected post and re-saving the custom field value (removing it and adding it again) stores it in the new format and makes it searchable.