Core

The problem seems to be that $uid is 0 in this case and therefor

$records = self::getRecordsByField($theColConf['foreign_table'], $theColConf['foreign_field'], $uid);

fetches each record that is NOT child of a container.
So the question is, why is getProcessedValue called with a 0 value here.

This is the definition of the method

/**
     * Returns a human readable output of a value from a record
     * For instance a database record relation would be looked up to display the title-value of that record. A checkbox with a "1" value would be "Yes", etc.
     * $table/$col is tablename and fieldname
     * REMEMBER to pass the output through htmlspecialchars() if you output it to the browser! (To protect it from XSS attacks and be XHTML compliant)
     *
     * @param string $table Table name, present in TCA
     * @param string $col Field name, present in TCA
     * @param string $value The value of that field from a selected record
     * @param integer $fixed_lgd_chars The max amount of characters the value may occupy
     * @param boolean $defaultPassthrough Flag means that values for columns that has no conversion will just be pass through directly (otherwise cropped to 200 chars or returned as "N/A")
     * @param boolean $noRecordLookup If set, no records will be looked up, UIDs are just shown.
     * @param integer $uid Uid of the current record
     * @param boolean $forceResult If BackendUtility::getRecordTitle is used to process the value, this parameter is forwarded.
     * @return string
     */
    static public function getProcessedValue($table, $col, $value, $fixed_lgd_chars = 0, $defaultPassthrough = 0, $noRecordLookup = FALSE, $uid = 0, $forceResult = TRUE) {

And these are different use cases and how it is called:

$defaultLanguageValue = BackendUtility::getProcessedValue($table, $field, $this->defaultLanguageData[$table . ':' . $row['uid']][$field], 0, 1);

$defaultLanguageValue = BackendUtility::getProcessedValue($table, $field, $this->additionalPreviewLanguageData[$table . ':' . $row['uid']][$previewLanguage['uid']][$field], 0, 1);

$diffres = $t3lib_diff_Obj->makeDiffDisplay(
    BackendUtility::getProcessedValue($table, $field, $dLVal['old'][$field], 0, 1),
    BackendUtility::getProcessedValue($table, $field, $dLVal['new'][$field], 0, 1)
);

As you can see they are using just 5 out of the 8 possible parameters, so $uid will always be 0, which is just plain wrong for the case of inline elements pointing to a foreign table.

I will move this to the core tracker.

This is not just about Gridelements, but AFAICS about any element using fields of type inline.

IMHO it should be enough to introduce a check for $uid being available in line 2080 of typo3/sysext/backend/Classes/Utility/BackendUtility.php, since we need to check that for existing uids only.

Patch set 1 for branch TYPO3_6-2 of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at http://review.typo3.org/31947