Here is a comment in ExecFindPartition() in execMain.c:
     /*
      * First check the root table's partition constraint, if any.  No 
point in
      * routing the tuple it if it doesn't belong in the root table itself.
      */
I think that in the second sentence "it" just before "if" is a typo. 
Attached is a small patch for fixing that.
Best regards,
Etsuro Fujita