Thanks for those responses, and links to examples. I went back and re-created the data grid and found that I had previously includes an CSS class element:

.dt-buttons.ui-buttonset    
       {
           display : inline-block;  
           width: 60%;   
        }    
  

Removing the 60% width statement rendered the buttons correctly on line. Sloppy cut-n-paste on my side, so thanks again.