csvjoin includes columns on which it joins twice

Created by: gn0

Using csvkit 0.5.0, I get the following output:

$ csvlook a.csv      
|-----+--------|
|  id | a      |
|-----+--------|
|  1  | lorem  |
|  2  | ipsum  |
|  3  | dolor  |
|-----+--------|
$ csvlook b.csv 
|-----+---------|
|  id | b       |
|-----+---------|
|  2  | asztal  |
|  3  | papir   |
|  4  | toll    |
|-----+---------|
$ csvjoin -d , -c id a.csv b.csv | csvlook
|-----+-------+----+---------|
|  id | a     | id | b       |
|-----+-------+----+---------|
|  2  | ipsum | 2  | asztal  |
|  3  | dolor | 3  | papir   |
|-----+-------+----+---------|
$ 

The output I expected:

$ csvjoin -d , -c id a.csv b.csv | csvlook
|-----+-------+---------|
|  id | a     | b       |    
|-----+-------+---------|
|  2  | ipsum | asztal  |
|  3  | dolor | papir   |
|-----+-------+---------|
$ 

Surely I'm missing something?