NVENC Async mode and picture-type decision

The documentation NVENC VideoEncoder API v4.0 , clearly states in section, that synchronous encoding, and enablePTD=1 are incompatible. However, the sample available in the SDK (HeavyHand_1080p.txt config for nvEncode.exe) has:

syncMode = 1
enablePtd = 1

Internally, these are actually set in the NV_ENC_INITIALIZE_PARAMS, does this mean these two are actually compatible in version 4.0 of NVENC? Or does it mean that it will eventually be set to a different value?

I would like to send the input buffers in display order (enablePTD=1) without having to handle asynchronous mode.