Wondering why /CONST: doesn't seem to work?

I have a number of SessionVars whose values I have set to design-time constants, like so:

%SessionVar% #SessionVarValue#

This works for the built-in design-time constants, like #ISODATE#.

The constants are first defined in the project with empty values, on the Constants tab. They are then also defined in constants.ini, with the actual desired values, like so:

[constants]
#SessionVarValue#=Desired value
...

At the commandline, from the folder containing the .SUF, I call SUFDesign so:

sufdesign /build /const:constants.ini <projectname.suf>

The project builds, and ends up where it is supposed to, but a Dialog.Message displaying the value of two of the SessionVars whose values I've set to the Design-time constants defined per above shows them to be empty.

Have I missed something?

thanks in advance!
DDoutelMS