NvEncLockBitstream always sets pictureStruct to 0

When I’m encoding using nvenc the NV_ENC_LOCK_BITSTREAM structure returned by NvEncLockBitstream always has the pictureStruct set to 0. The comments in the code suggest it should return a NV_ENC_PIC_STRUCT. I can just keep track of it in my own code, since it will be constant across all frames, but this seems like a bug.