We have sent jobs to computers to make them boot to automation, and sometimes it works, but sometimes it simply goes to production with a PXE-M0F.  Same thing happens when there are no jobs assigned.  Sometimes things work, but often F8 isn't even an option.

None.  However, in the SBSLob_PXE log, there is a message indicating that it couldn't parse the response from the server, like this:

NS response parse failure, bytes read 247, 'HTTP/1.1 200 OK
Cache-Control: private
Content-Length: 85
Content-Type: text/xml; charset=utf-8
Server: Microsoft-IIS/7.5
X-AspNet-Version: 2.0.50727
X-Powered-By: ASP.NET
X-Frame-Options: SAMEORIGIN
Date: Tue, 31 Dec 2013 17:20:56 GMT

We're not quite sure the absolute cause, but we're confident it is from something in the network stack that is splitting the response packet.  A good packet is longer than this - this is only part of the response.  Because the rest of the data comes later, the PXE Server service is unable to figure that out.  When it gets no "valid" response, the fail-over for PXE is to send the system to production/Next Device.

There is a point-fix available in support if you are getting partial responses.  HF3 for the GA release of DS 7.5 should also include this fix.