counter and Usage is broken?

Hello, I am Using ASCIIDOCTOR 1.5.6 and  the "usage" to suppress the output is not working

any help or hint?

[caption=""]
.Parts{counter2:index:0}
|===
|Part Id |Description

|PX-{counter:index}
|Description of PX-{index} {index:usage}

|PX-{counter:index}
|Description of PX-{index}
|===

produces

Parts
Part Id Description
PX-1        Description of PX-1 {index:usage}
PX-2        Description of PX-2