[TYPO3-english] flexforms addPiFlexFormValue() is ignored

[Muriel le Pair]

Hi,

I'm still strugling with the migration of an old extension to extbase.

I have created an extbase extension with the extension builder and would 
like to add some flexforms in the BE some how the settings are ignored.

I have added the flowing code to ext_tables.php:
// you can exclude some fields form backend-rendering - it have nothing 
to do with your extension
$extensionName = t3lib_div::underscoredToUpperCamelCase($_EXTKEY);
$pluginSignature = strtolower($extensionName) . '_pi1';
$pluginSignature = $_EXTKEY;

// Disable, activate the display of the plug-in flexform field and set 
FlexForm definition
$TCA['tt_content']['types']['list']['subtypes_excludelist'][$pluginSignature] 
= 'layout,select_key,pages';
$TCA['tt_content']['types']['list']['subtypes_addlist'][$pluginSignature] = 
'pi_flexform';
\TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addPiFlexFormValue($pluginSignature, 
'FILE:EXT:' . $_EXTKEY . '/Configuration/FlexForms/flexforms_be.xml');

addPiFlexFormValue() should add the BE flexform, but is somehow ignored.

When I add the following line a copy of the original extension is added 
in the extension list with the name 'test' and the flexform works fine 
with 'test':
\TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addPlugin(array('test', 
$pluginSignature), 'list_type');

So what am I missing?

--
kind regards,

Muriel le Pair