It could have been my colleague triggering this capability. When we switched from CATIA V5 NC to NX CAM, we had to create mapping rules to bring about 2000 boring bar like tools of a single internal customer from our in-house tool database to NX. In order to get tool shapes as realistic as possible my colleague choose the step drill tool type as target class, because he didn't like the OOTB boring bar. Siemens improved the step drill tool type for US to support more geometric capabilities.
Fortunately, Siemens continually improves its tool types and we can migrate from this misuse to the desired tool types.