What I do wrong using Date field argument with ?

Hello! There's no found solution seeking for documentation and issues.

I'm trying to show nodes grouped by months via Date type fields by view:

Adding argument "my_date_field" (and "Date: Date (node)" - I tried both): When the argument not presented: Summary, sorted descending; Basic Validation; Granularity: Month; Date fields: my_date_field; Method: OR.

So I get my nodes grouped by months (each month has own page like '/mypath/2012-05'): the page with months list and the pages with nodes that have my_date_field values according to selected month.

All works good until I don't add Date filter with the same field: Operator: less than; Date default: now. Then list of months display correct (months till last month), but clicking on one of month we getting all nodes not accordingly chosen month (for example, if we trying to see May, 2012, there will be all nodes on this page by all monthes and all years).

Great Thanks!

P.S. Sorry for russian in view export file.