A method was proposed in this journal (vol. 6, no. 1, pp. 192-201, 2007), which tackles a power allocation problem for interleave-division multiple-access (IDMA) systems over fading channels. In this paper, we show that the method may not provide valid solutions in some situations. We illustrate this with many numerical examples. Our findings indicate that the method should be applied carefully, and further investigation is required to find efficient methods for more general situations.