conditional formatting not working for every row in a table

I have a text field called "Status" and I have created a numeric "Status Numeric" as follows:

if [status] = "Not Started" then 1 else if [status] = "Past Due" then 1 else if [status] = "In Progress" then 2 else if [status] = "Passed" then 3 else 0, Int64.Type

Because it is not possible to apply conditional formatting to a text field (or is it?), I have applied it based on the value of "Status Numeric":

and this is where the problem occurs. Some of the "Status" fields are formatted correctly, some aren't: 

and there seems to be no pattern. 

I wonder if it's something to do with the "Sum" element of the conditional format: 

but, if it isn't, I have no other ideas.