HP Instant Capacity User's Guide for versions B.07.x

Special Considerations
Instant Capacity Compatibility with Processor Sets
Appendix A142
With vPars version A.04.01 or greater, vPars is Pset-aware to an extent.
When adding processors to a running vPar, a processor is always added
to the default Pset; thereafter, it may be moved to another Pset. When
removing processors, vparmodify will choose processors from the default
Pset first, and if not enough exist in the default Pset to satisfy the
request, vparmodify chooses the remaining processors arbitrarily,
without regard to Pset membership.
With vPars versions less than A.04, no special consideration is given to
Psets from the vparmodify command’s perspective. Therefore, when
using vPars, processors in non-default Psets must be bound processors.
Otherwise, a processor designated for deactivation by vparmodify may
be selected from an unexpected Pset.