that must be some other bug ?
This was definitely bookerly only (a change of font on the kindle from within the book would remove it/ bring it back) and it was with converts from epub to azw3 made in calibre then USB loaded. ( not emailed to amazon ).
if you backtrack up to the reddit discussion link , that in turn links to an excellent side by side picture of the "bug" being present in bookerly and not present for the same page in some other font
I think, from reading the older mobileread thread, that having
text-align: justified; in the paragraph css could have been the trigger. I could not find an example of the behaviour in a bought-from-amazon book + downloaded-directly-to Kindle book and I hypothesise that amazon's own original css does not typically include such declarations
but for me the issue has now disappeared with the latest firmware, in the books I am reading and in the little test epub I made
Code:
<body class="calibre">
<p class="block_">Test book</p>
<p class="block_">“Alpha”</p>
<p class="block_">“Bravo”</p>
<p class="block_">“Charlie”</p>
<p class="block_">“Delta”</p>
<p class="block_1">*</p>
</body>