With the vanilla engine fix, my bots always need two trips for any mining drill (or two bots get busy instead of one). It's not the end of the world, but it is… annoying. Because this also means my inventory gets filled (slowly, granted) with ore I don't want there.
As slight delay would, I'm pretty sure, fix it, or most of it (of course, if the Lua API supplies info on whether ore is still to be put on a belt, that would be preferred).