The MPI_File_iwrite() functions in some MPI builds will use the AIO interface to carry out the I/O operation if the datatypes are all contiguous. In this case Darshan correctly reports statistics from the MPI-IO level but fails to report any POSIX write operations.

Attached modified version of i_noncontig test program demonstrates the problem. Confirmed with MPICH 3.0.4. Note that the test program generates a large number of errors upon completion (with or without Darshan) because it has been deliberately modified to trigger the Darshan bug without regard for program correctness.