Hi François,
I'm glad you figured it out! Indeed, the script generation of this specific type of process options generated the value as a string rather than a cell. Adding the brackets to your existing scripts will do the trick, and the following commit should fix the issue for newly generated scripts: https://github.com/brainstorm-tools/brainstorm3/commit/a3274d0f6b5f6675f8659ef9d616bc854a1d0c5a
Thank you for reporting this issue!
Martin