hm. it can be only if we turn of done tag and set dateformat as empty string? It is strange that somebody do this but if so - there is one much more bigger problem - I can set date form like this {%y-%m-%d %H:%M} and nothing will work.

My opinion is - we need to open an issue and discuss about this problem. If you don't mind I will not include your modifications in commit. We will attach this case to future issue.