You should avoid using the sort buttons.

Instead, you should highlight the complete range that you want to sort
(CTRL_A will often get this okay), then use Data | Sort. You can now
specify which column to sort on (up to 3 columns) and whether to sort
in ascending or descending order. You can also specify if your range
begins with a header row - which will be the reason for everything but
the first item being sorted if you use the buttons.

Hope this helps.

Pete