Incorrect calcluation of proportions

I'm using Beta 3.13. When I enter data for a one-arm binary study, the Proportions are not always calculated correctly. Specifically, when the number of treated events is zero, the proportions are wrong. For example, I entered a study with 27 subjects and 0 events. The calculated proportion was given as 0.018. In another case, with 0 events among 240 subjects, the proportion was 0.002.