I don’t think it’s a bug. As a String, it does its job.
But if we had one that returns number, we could do better operations on that tag. It would be a simple change(just return number instead of string Eg:- 5 for “+5”, 5.5 for “+5:30”, 5.75 for “+5:45”, -5 for “-5” etc) on the Watch Face studio app, but a big advantage for us watch face developers.
Hope I am making sense and can be implemented.