B777 and Cloud,
My post was unclear. What I was saying is that it is Boeing policy on disconnecting the AP on a single channel app to also disconnect the autothrottle, so when the pilot disengages one, he will also disengage the other, so full autoflight or full manual. The exception to that policy is when conducting a GA from a single channel app, where TOGA applies TOGA thrust through the autothrottle but disengaged the AP (AP remains engaged only on dual channel app). So, in a missed app, the pilots now have the unusual cicumstances of manual flight with autothrottles, which then sets them up for the trap with the AT mode problem on Alt Aqu. I did not say the AT disengaged on pressing TOGA.
For what it's worth, some companies do things contrary to Boeing guidance, as B777 said. Excel used to do dual channel for every ILS, though that brings in trim issues for low disconnects for manual landing, and would deselect speed of the MCP AT when flying manually. Seemed a smarter way of doing thins, IMO.