Until Amazon fixes this I don't believe it is possible to find a reliable solution which works with all devices.
You mean using anchors
As long as the href for the "text (or start)/toc" reference items in the OPF's guide section points directly to an (x)html file (with no url fragments involved), all my ebooks' Start Points behave exactly the same in the Kindle Previewer as they do on a KF8-capable Kindle Keyboard device.
, however, reproduce your exact issue (on the Kindle Keyboard) by introducing anchors and url fragments into the mix. So it seems to me that the "fix" is a bit obvious. But perhaps I'm not fully understanding.