I don't know if this is a Mac issue, or a general issue.
I also don't know if it's a bug, if it's me missing a setting somewhere, or if it's lack of liturgical knowledge on Logos' part, but my lectionary (the Catholic one) only shows the right Sunday one day a week, i e on the Sunday itself. The rest of the time it shows the following Sunday, not the preceding one, like it should. The Christian liturgical week, just like the Jewish one, starts by sundown on Saturday, and that's when the lectionary should switch. This way I'll be told it's Easter Sunday all through Holy Week...