Unwanted sort by date

Hi there...
When I open Calibre, there's a problem with the sort order.
My standard sort order is as follows:
==> Title, Series, Author, Read
The latter field is a customized date field to indicate if/when I have read the book. This way I have all the read books on top, followed by the non-read ones, sorted by Author, then by Series, then by Title.

Now, when I open Calibre, the books are ordered as follows:
==> Date, Series, Author, Read
This way, the non-read books are sorted by Author, then by Series, then by Date -- not by Title.

I somehow think this behaviour must have crept in with one of the recent versions, but I'm not sure.
Any tips on how to fix this? TIA.