This is actually a feature to help you find the best player for the position you are needing to fill. When you perform a player search by position, it will actually evaluate all players for if they were switched to that position. The position in parentheses is the position they are currently assigned at, but you are looking at the bars that are applicable for the position you had searched for. This gives you a pretty good look at what that player would look like if you moved them to the position in question.
The strange results you are currently getting are due to the fact that most of the available players right now are really not any better at their assigned position than they might be if moved to another position, because pretty much all players that are worth having on your roster have been drafted. If you search by an attribute, it will further skew the results. You also might just find a gem mis-assigned to a position.