Error while generating NLO events with polarized e+ e- beams

Dear Whizard team,

I am trying to generate events (using whizard for showering with POWHEG matching, pythia8 for hadronization) at NLO (in QCD) for e+ e- > t tbar with polarized incoming beams, but I am getting the following error:

******************************************************************************
*** FATAL ERROR: Product of density matrices is empty
*** --------------------------------------------
*** This happens when two density matrices are convoluted
*** but the processes they belong to (e.g., production
*** and decay) do not match. This could happen if the
*** beam specification does not match the hard
*** process. Or it may indicate a WHIZARD bug.
******************************************************************************
******************************************************************************

The input script "ttNLO.sin" along with all the associated ".log" files are attached here: https://www.dropbox.com/sh/j1istyiiwptaohu/AAAlyCLa0taG3HpljPltrTTBa?dl=0 .

Actually, I was able to generate NLO events for the same process using unpolarized beams, and LO events using polarized beams, so I am not sure if this is a bug?

Any help would be greatly appreciated!

Thanks a lot,
Prudhvi