Thread: BeforeNavigate2 event and PostData

I'm capturing the BeforeNavigate2 event of a WebBrowser control and I tried to edit the PostData parameter from here, but it won't send my updated data (just sends the original PostData).

Code:

void BeforeNavigate2(IDispatch *pDisp, VARIANT * url,VARIANT * Flags,VARIANT * TargetFrameName,
 VARIANT * PostData,VARIANT * Headers,  VARIANT_BOOL * Cancel) 
{
		SAFEARRAY* psa = (SAFEARRAY*)SendMessage(msgForward, WM_USER+0xdead,
			(WPARAM)0, (LPARAM)PostData->pvarVal->parray); //retrieves modified post data into psa
		SafeArrayCopyData(psa, PostData->pvarVal->parray); //applies the modified data
}

I've made sure it all works in debugger, isn't this the place where modifications of PostData before request can be made?