Date filter only works on `{{datetime}}`

[basepi]

According to the documentation, you should be able to do {{date|date('Y-m-d')}}. However, this doesn't work; the output is blank. {{datetime|date('Y-m-d')}} does work, but I want to be able to do this with {{highlight_date}} and other similar variables.

Anyone have any hints on how to get this to work? Can I convert the {{highlight_date}} to a datetime object, somehow?

Thanks in advance!