Notice: String offset cast occured in _field_invoke_multiple

Any clue what's causing this?
All I have in my case is simply module enabled. Did not do any configure any validation on fields at all yet.

Notice is raised if PHP 5.4+, due to a pending bug in core, see https://drupal.org/node/1824820 .
Until it is fixed, try this workaround: add these 3 lines before line 195:

<?php

    // Workaround for core bug #1824820 until it is fixed.
    // Entity language should be passed as array for not raising a PHP notice
    // in some cases, only if PHP 5.4+.
    $info = entity_get_info($entity_type);
    $cloned_entity->{$info['entity keys']['id']} = 0;
    $cloned_entity->language = array(0 => $cloned_entity->language);

    $element += field_view_field($entity_type, $cloned_entity, $field['field_name'], $display, $langcode);

?>

We need this patch to be added to our devtrac install profile.

So here's that patch.

#1824820: String offset cast notice in field_invoke_method_multiple() was fixed in Drupal core, so this should only be needed on unsupported versions of core. Plus, it causes its own notice(s) on forms for entities that don't have the language property (e.g. terms), so would have needed further work anyway.