My recent studies of para-benzyne radical anion has shown that relative energy difference between C_2v and D_2h structures calculated at DFT level of theory are proportional to the electron self-interaction error included in DFT potential. The more HF exchange DFT potential has the smaller is the electron self-interaction error. Thus the most common B3LYP potential places D_2h structure lower in energy mostly because of the electron self-interaction error.