Sorry for the little late reply. Like all developers around the world, some of our crew members are on vacation; but it will be ended soon and we will be prompt again replying forum questions.
-> You have to disable the "chosen" plugin, so MaterialMart will get the control over dropdown select box. To disable chosen plugin, navigate to Virtuemart Backend >> Configuration >> Templates and disable this option:
- Use jQuery chosen for dropdowns in FE
Then, you should no longer see those kind of duplications.