TYPO3 Core

Registered Page TSconfig files can be included in arbitrary pages by selecting the items in the field "Include Page TSConfig (from extensions):". In the function \TYPO3\CMS\Frontend\Controller\TypoScriptFrontendController::getPagesTSconfig() these includes are not taken into consideration.
In the corresponding BE function \TYPO3\CMS\Backend\Utility\BackendUtility::getPagesTSconfig() the includes are included.

If you include a registered TSconfig file with linkhandler configuration the new tab appears in the backend, but the link won't be rendered in the frontend because the TSconfig is missing.