Unknown or missing input/output interface index on VRRP members

I am experiencing this issue when sampling on an interface which is a member
of a VRRP instance on a HP PROCURVE 5412ZL.

With traffic coming in on interface A and leaving on interface B, where B is
part of the VRRP instance,
the output interface written in the flow samples is this:

sflow.fs.ifindexout == 0x3fffffff

Which according to the specification indicates that there is no output
interface.
The same behaviour applies in the other direction, where traffic is incoming
on interface B and leaving on interface C (which is not a VRRP member).

I was wondering if anyone experienced any similar issues before I report
this to HP.

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Cheers,
Rune V. Sjoen
You always pass failure on the way to success