The Makefile.am files scattered about the build tree use wildcards (e.g. src/main/include/log4cxx/Makefile.am) which is a no-no (https://www.gnu.org/software/automake/manual/html_node/Wildcards.html). On a VPATH build, not including $(top_srcdir) and $(top_builddir) when looking for headers with *.h causes generated headers to not be installed (e.g. log4cxx/log4cxx.h!). On a non-VPATH build, including both causes duplicates in the installed file lists (as $(top_srcdir) and $(top_builddir) coincide) and can break installation a la LOG4CXX-385.
The Makefile.am files need to include explicit header lists.