I have one column that don't appear to be sorting correctly.  I can't sort by serial number by clicking on column name. It appears sorting random. Talking about other columns like quantity or product_creation_date everything is allright I can sort desc/asc by clicking on quantity or product_creation_date columns.

This screenshot might help a bit:

[URL=http://www.part.lt/perziura/33fb83e565675a095822de6b56b0d1ae434.png][IMG]http://www.part.lt/img/33fb83e565675a095822de6b56b0d1ae434.png[/IMG][/URL]