TYPO3 Core

$GLOBALS['BE_USER']->adminPanel->extGetFeAdminValue('preview', 'simulateUserGroup');
or
$GLOBALS['BE_USER']->adminPanel->extGetFeAdminValue('preview', 'simulateDate');

returns 1 if they set to 0

In ->extGetFeAdminValue it will return the value from override.preview = 1 if e.g. 'override.preview.simulateUserGroup' is not set, empty or 0

I think asking for 'override.preview.simulateUserGroup' and returning 'override.preview' is a wrong behavior.

admPanel {
    ...
    override.preview = 1
    override.preview.simulateUserGroup = 0
    override.preview.simulateDate = 0
    ...
}

My Reasons for that:
With EXT:simulatebe i have an FE User and BE User online. The Adminpanel is hidden. To Respect the Usergroups from the FE User I have to set simulateUserGroup to False but will have the preview = 1 at the same time.

The same with simulateDate. I show content that depends on $GLOBALS['SIM_EXEC_TIME'] but this is always '1' when I logged in and have editing rights.

Fix: Change

if ($val && $GLOBALS['BE_USER']->extAdminConfig['override.'][$sectionName . '.'][$val]) {

in /typo3/sysext/frontend/Classes/View/AdminPanelView.php to

if ($val && isset($GLOBALS['BE_USER']->extAdminConfig['override.'][$sectionName . '.'][$val])) {

If nothing is set the behavior is like before (so i assume nothing will break), but it returns not '1' if '= ' or '= 0' is set.

This is a bug in older t3cms versions too.