The pitchers don't do a good job of holding the runners. Jason Johnson was the worst one before they got rid of him. V Mart is bad though. From what I've seen of him, he has a 1 second delay when he cocks his arm back, before he releases the ball. Maybe they need to work with him on his throwing mechanics, or just move him to 1B altogether. I think its a combination of the pitchers not holding runners, and V Mart just not having a strong enough arm.
As of right now, it appears V Mart will play 1B when the Indians play a Lefty. Look for him to start at 1B tonight vs The Big Unit!