You may want to check the field "type", if it's set as a number instead of text, this may explain the behavior.
I would even try creating a new calculation field (resulting in a number) that gives a 1 if the field is "T" else, 0. Then sort on the calc field to see what happens.
You are correct. The type is number. So when FileMaker imports FoxPro logical fields, it creates them as numeric fields, but the value imported is either "T" or "F". This is confusing. Do you know if this is documented anywhere? If not, I guess I'll need to experiment.
I already had a calculated field based on this field which would display a checkmark (option-V) when the value is "T" [If (Prepared = "T"; "√"; "" )] and that is working.
Thanks for pointing me to the field type.