Spotfire unexpected result using Over with Intersect & Previous - spotfire

Question

I'd like to create a new column with values taken from a previous row. The rows are tagged by "ID" and are ordered by "Depth" in the original table. This is the custom expression that I think should do it, but I'm getting unexpected results where some rows aren't picking up a value from the previous row.
Max([Value]) over Intersect([ID],Previous([Depth]))
Here's an example table with my expected results and the actual result given by the expression above.
ID Depth Value Expected Actual
Object1 0 0.02
Object1 3033 68.87 0.02
Object1 3349 70.82 68.87
Object1 3538 70.65 70.82
Object1 3791 70.38 70.65 70.65
Object1 4044 69.31 70.38 70.38
Object1 4297 71.13 69.31 69.31
Object1 4549 70.9 71.13
Object1 4802 70.59 70.9
Object1 5055 71.56 70.59
Object1 5307 71.34 71.56 71.56
Object1 5560 71.32 71.34
Object1 6381 71.5 71.32
Object1 6444 71.62 71.5 71.5
Object1 6544 71.86 71.62 71.62
Object2 0 0.02
Object2 962 267.58 0.02 0.02
Object2 1024 276.67 267.58 267.58
Object2 1213 273.11 276.67 276.67
Object2 1529 275.56 273.11 273.11
Object2 1593 275.96 275.56 275.56
Object2 1656 275.15 275.96 275.96
Object2 2854 278.35 275.15 275.15
Object2 3107 276.45 278.35
Object2 3359 270.83 276.45
Object2 4370 272.89 270.83
Object2 4623 271.93 272.89
Object2 4877 269.93 271.93
Object2 5504 270.51 269.93
Object2 5538 270.38 270.51 270.51
Object2 5541 270.37 270.38 270.38
Object2 5688 269.8 270.37
It seems to me that the issue might have something to do with the ordering of the Depth column. As a workaround, I can successfully get the expected result if I first calculate a rank column (call it "RankColumn")
Rank([Depth],[ID])
Then I calculate the over statement using the calculated rank
Max([Value]) over Intersect([ID],Previous([RankColumn]))
First question: why didn't Spotfire recognize the order in the original Depth column?
Second question: if conducting the intermediate rank calculation is a necessary step, is there a more elegant way to write the expression (e.g. do it in one expression rather than creating an intermediate column)?