Date options not available on filtering summarised and cast dates

I have some data with dates stored as text. Unfortunately I can't change the data type in the source database. So I cast the text to dates in the table metadata admin pages and now I can use the date filters (e.g. last 12 months, etc) in my questions. I can also summarise the data using date options (e.g. grouping by week, day, minute, etc). Yay!

However if I take summarised results e.g. max(date) I can no longer use the date options to filter those results.

Conversely, if I try using a field in the database that was originally stored as a date, not text, then I can use the date options all the time.

So it seems like it converts from text, to date and then back to text again after summarising the data.

Has anybody come across this before? Any suggestions would be gratefully received.

I figured out a workaround in case anyone else gets stuck with this. Create a new question based on the original question and,hey presto, the date options will be available for you to filter on.