I have noticed that when referencing a module that has Time as a dimension from a module that does not have it as a dimension that the formula will not return the highest node in the Time Dimension
E.g. I have a Module with Employees & a Boolean line item and a Module with Employees & Time (with Summary as Sum) & a Number line item. If I enter a value into any of the Employee/Time intersections it will roll up to the 'All Periods' Time dimension. But if I then reference that employee from the original Module it will not return the All Dimensions value
I'm assuming I need to use SELECT:Time.'All Periods' in these circumstances?
Just adding to what Nathan said – the reason for this is that although All Periods acts in some ways like a top level item, in other ways it acts like an orphan item in the time dimension. You can see this when you open a page selector – if it were a true top level item, you'd see the years rolling into All Periods, but instead you see All Periods as a detached item in the tree.