Why does the stamp on the left look 'funny'? Is this a rough paper variety, perhaps? Compare it to the one on the right. Both are single watermark printings, but the one on the left looks so much cruder that at first I thought it might have been a forgery.
By the way, the one on the right is postmarked '---DERA.' Any suggestions as to what the placename would be, other than Narrandera, which seems too long to fit, and Undera, which seems too short?