When creating Part Boundaries with Plane set to 'Specify', only the first boundary is created on the specified plane.
Solution
The problem is fixed in NX 1953.
As a workaround in NX 1946, create the additional part boundary sets. These will not initially be created on the specified plane.
Select the incorrect boundary sets, and click on 'Inferred'. This will then move the boundary sets to the correct plane.
Hardware/Software Configuration
Platform: INTL64
OS: windows
OS Version: 10_1909
Product: NX
Application: CAM
Version: V1946
Function: BOUNDARIES
Ref: 002-8523687