TYPO3 Core

I noticed, that at least in two extension in my test system (FLUX and tx_damttcontent) there were errors in the page module display in the backend,
that had the same structure:

<MyExtensionHookClass>::preProcess() must be compatible with that of TYPO3\CMS\Backend\View\PageLayoutViewDrawItemHookInterface::preProcess()...

I looked into both extension hook classes and found the parameters be the same and are matching the interfaces' declaration:

Extensions preProcess() parameters: tx_cms_layout &$parentObject, &$drawItem, &$headerContent, &$itemContent, array &$row
Core Interface Class requirements: \TYPO3\CMS\Backend\View\PageLayoutView &$parentObject, &$drawItem, &$headerContent, &$itemContent, array &$row

the tx_cms_layout object type is also mapped on the right namespace path.

Can anybody investigate, why this error occurs although the preProcess-functions in the extensions have the right declaration ?

I consider this a major issue for all extensions that hook into the backend page module.