[Haskell-cafe] Neither of the sparks are converted into OS threads but parallelization happens surprisingly!!!

Dear List, I have a point misunderstood! I am using second generation strategies of Haskell to parallelize some number of algorithms in Haskell. The missing point here is that: In some cases, neither of created sparks are converted into OS threads, but parallelization happens surprisingly, when I use threadscope to see what had happened during the evaluation. What happened to me was that 2 sparks were created one of which was pruned, none of which was converted into OS threads and the last one was missing, however, parallelism happened!!! I wonder what is the reason for this? Could someone aware, please shed light on the issue? Thanks in advance. Saluti, Burak.