It's a known bug with Kindle devices. It's even exhibited in the Kindle Previewer. The way to avoid it is to put your anchor point before/outside of
the element you're trying to link to.
Consider this end-note link encountered in the text of a document:
This anchor point (target) can exhibit the issue you're seeing:
<p id="endnote1" class="endnote">This is my first endnote.</p>
This is what you need to do to make sure it doesn't happen:
<a id="endnote1" /><p class="endnote">This is my first endnote.</p>
<a id="endnote1"></a><p class="endnote">This is my first endnote.</p>
My example isn't exactly
like your backlink, but the principle is the very same: put the anchor you're linking to before/outside of
the element (p, h1, h2, h3, etc...) you're shooting for.