did you set a Startup tweak?
Code:
ID: sort_columns_at_startup
Provide a set of columns to be sorted on when calibre starts
The argument is None if saved sort history is to be used
otherwise it is a list of column,order pairs. Column is the
lookup/search name, found using the tooltip for the column
Order is 0 for ascending, 1 for descending
For example, set it to [('authors',0),('title',0)] to sort by
title within authors.