Previous work has identified iterative multiuser decoding techniques that are often only limited by theoretical channel capacity. These investigations usually dealt with the case where user waveforms are decorrelated to some degree. Investigations with identical waveforms indicate that the theoretical capacity limits are not always achieved. Performance has a threshold-like behaviour, as one might expect with a capacity limit, but the threshold is, in some cases, above the theoretical capacity for the channel under investigation. In this paper, an explanation for this behaviour is proposed.