Edit date format selections not being applied correctly?

Is anyone else seeing this?

Changing the date format in the 'edit template' screen allows me to select a different format, but the new format is:

• not applied to the preview
• not retained if I leave / return to this screen
• not applied to the live site (confirmed with debug function, where dateFormat in JSON remains original value)

The template is unmodified and correctly uses {{date}}. Other changes in the edit template screen (such as font, font size and line spacing) are correctly applied.