Duplicated field "layout" in TCA (tt_content)

We've got a duplication of the field "layout" in our TCA of tt_content which is present in fluidcontent elements (e.g. flux) only.
It's generated at line 44 in your Configuration/TCA/Overrides/tt_content.php file (https://github.com/FluidTYPO3/fluidcontent/blob/development/Configuration/TCA/Overrides/tt_content.php#L44):

$GLOBALS['TCA']['tt_content']['types']['fluidcontent_content']['showitem'] = ' --palette--;' . $frontendLanguageFilePrefix . 'palette.general;general, --palette--;' . $frontendLanguageFilePrefix . 'palette.header;header, --div--;' . $frontendLanguageFilePrefix . 'tabs.appearance, layout;' . $frontendLanguageFilePrefix . 'layout_formlabel, --palette--; '. $frontendLanguageFilePrefix . 'palette.frames;frames, --palette--;' . $frontendLanguageFilePrefix . 'palette.appearanceLinks;appearanceLinks, --div--;' . $tabsLanguageFilePrefix . 'access, --palette--;' . $frontendLanguageFilePrefix . ';visibility, --palette--;' . $frontendLanguageFilePrefix . ':palette.access;access, --div--;' . $categoryTabLabel . ', categories, --div--;' . $tabsLanguageFilePrefix . 'extended, --div--;LLL:EXT:flux/Resources/Private/Language/locallang.xlf:tt_content.tabs.relation, tx_flux_parent, tx_flux_column ';

By removing layout;' . $frontendLanguageFilePrefix . 'layout_formlabel,, it works fine and gives us the right result as it should be: https://github.com/egtgm/fluidcontent/commit/c3409dc40bd627a26dcfa80ca6eb14591c8ac857

TYPO3: 8.7.2
fluidcontent: 5.2.0
PHP: 7.1.1

[fnagel]

Same issue here. A similar issue is fixed and worked around using the CompatibilityRegistry in flux, see FluidTYPO3/flux#1352