Most tasks in my MPP use the standard calendar, a few use a calendar I've created called "Weekends included" (where saturdays and sundays have been made non-default working time, 0800 - 1200 and 1300 - 1700).

The tasks are assigned correctly to the calendars.

2 of the tasks assigned to the weekends included calendar are dependant.

The predecessor is a "0d" milestone and is constrained to start no earlier than Sunday (in this case 7/3/10). There is no lag in the dependancy. There is no constraint on the successor, which is a "2h" duration task.

Having magnified the GANTT view, the predecessor does indeed occur on Sunday at 0800, but the successor then waits until Monday at 0800 to start (I expected it to occur between 0800 and 1000hrs on Sunday).

What have I done wrong?

I would've expected the