Problem With Gearman Job Status

I have a Gearman server running a process which takes a few minutes to finish. I'm running a progress bar to show completion, and am attempting to get the percentages for the bar using the Gearman PHP extension and the jobStatus() function.

The job is definitely active and found, as the first two fields (known + still running) return to true. However the third and fourth fields (numerator and denominator of completion percentage) return with nothing. Does anyone know why this might be or how these numbers are computed?