TYPO3 Core

The feature to simulate a date / time with the admin panel is broken under some circumstances.

This happens, as the "hidden" and the field that only "displays" the date / time have the same name but for the "display" field appended with "_hr".
You end up with:

hidden field name:

TSFE_ADMIN_PANEL[preview_simulateDate]

field name that just displays the date / time

TSFE_ADMIN_PANEL[preview_simulateDate]_hr

In some environments (combination of webserver, security modules, reverse proxy for caching, etc.) those parameters are combined in the request or modified in a way, that the value of "TSFE_ADMIN_PANEL[preview_simulateDate]" is the value from the "display field", which leads to be broken system in the frontend. As those settings are stored in the backend user profile in the database, the only way to fix is to reset the user settings, otherwise the frontend will be broken with the logged in user in the backend.