Workflow Parallel Foreach flow controls including client-side activities not respecting variable thread-locality

I have a lovely workflow that we're developing for a client which uses parallel foreach loop to execute some queries and  (maybe) produce reports.  I was having some report issues, so threw in some external log activities to watch what was going on.  When I did this, I began encountering odd behavior which was eventually discovered to be my querys' returned featureset variable getting accessed by EACH of my parallel processes in tandem, that is, I now have one featureSet instead of, say, seven distinct featuresets (one for each n in list(of n)).

 

Is this expected behavior that I am simply not understanding, and if so is there anything that I can do within the parallel scope to force this local variable to stay where it belongs?  Again, the logic runs fine without the logging acitivity, so I suspect that this is related to serialization.  Am I forced to avoid client-side activities within this kind of loop?