Linux Sigil Users Only!
There's a bug in libxml2-2.9.3 and higher that affects how QtWebKit renders html entities. Which means Sigil is affected on systems which use those versions.
To quickly tell if your system is affected:
Type a visible html entity (like ©) into Sigil's Code View (epub2). If it appears twice in Sigil's Preview or Book View, then you have the buggy version of libxml2.
I've released an executable, makeself Linux-only "updater" that installs a patched version of libxml2 into an existing Sigil installation to work around the issue.
NOTE: At no time will your system version of libxml2 be altered/affected by this update.
Download the installer (make sure it's executable bit is set) and use:
sudo ./sigil_libxml2_update.run
to install.
You'll have the option to bail out if you get cold feet.
See the Github README for more options/explanations.