$ ls /usr/share/doc/gtk-engines-murrine* ls: cannot access /usr/share/doc/gtk-engines-murrine*: No such file or directory gtk-engines-murrine doesn't install any documentation, while there are AUTHORS, ChangeLog, CREDITS, NEWS and README files available in the tarball. Some of these might be useful to install to /usr/share/doc/${P} with dodoc. NEWS and README don't seem so useful in the latest version, though. ChangeLog is very useful and is what I was looking for but didn't find in /usr/share/doc/${P}.
I'm not going to have access to a dev box for a bit, so feel free to make the change.
Fixed in 0.53.1-r1