Tested 0.5.1 and not quite ready for release yet. At this point, I would suggest deep-sixing the PrettyPrinter plugin. It looks as if it is going to take a lot more effort to fix all the issues with it for a minimal return.
If anyone is interested in testing the changes in the built-in PrettyPrinter, install Sigil from this link:
Sigil-2.7.6-Windows-x64-Setup.exe and replace the prettyprinter.xml file in C:\Users\<username>\AppData\Local\sigil-ebook\sigil\ with the one in message #42 in this thread.