TYPO3 Core

For all configurable backend images and logos in ext:backend extension configuration e.g. loginLogo or _ loginBackgroundImage_ the defined path get resolved by a custom method `getUriForFileName`.
This method calls, among others, GeneralUtility::getFileAbsFileName by providing the path with replacing a possible leading slash.

This is not done for the backendLogo field. Therefore it's not possible to enter a path with leading slash in contrast to the other settings.
As this is not explicit allowed or disallowed it should be unified with the other configuration fields.