Can not use custom Layout file, settings in layoutRootPath/s are ignored by YAG

[Moongazer]

Hello everyone, I try to customize the yag/Resources/Private/Layouts/Default.html like I usually do it with Fluid. So I've created an own extension with yagCustomTheme/Resources/Private/Layouts/Default.html, made some changes in this file and integrated a setup.txt with the following TypoScript in my extension:

plugin.tx_yag.view.layoutRootPath = EXT:yagCustomTheme/Resources/Private/Layouts/
module.tx_yag.view.layoutRootPaths.10 = EXT:yagCustomTheme/Resources/Private/Layouts/
# test it also for fluidContent, just to make sure:
lib.fluidContent.layoutRootPaths.10 = EXT:yagCustomTheme/Resources/Private/Layouts/

But it doesn't matter what I do, the overwriting of files works only for partials and templates, but my custom Default.html file is ignored completly! The TypoScript Object-Browser says, all layoutRootPath/s are overwritten successfully, but YAG still uses its own Default.html.

I've even tried do rename the layout "Default" to "MyCustom" and changed the template file to <f:layout name="MyCustom" /> to see where YAG is looking for the file after overwriting its paths. On the following error message you see that the TypoScript path settings are ignored and YAG still looking in its own Layouts folder:

Oops, an error occurred!
The layout files ".../typo3conf/ext/yag/Resources/Private/Layouts/MyCustom.html", ".../typo3conf/ext/yag/Resources/Private/Layouts/MyCustom" could not be loaded.

Is this a bug? Can someone confirm that its not possible to overwrite/customize the Layout file? Thanks for your help.