It's funny you say that, because the build fails here with my yakkety schroot with 1.2.4-1ubuntu1:

make[5]: Entering directory '/<<PKGBUILDDIR>>/properties/tests'
gcc -DHAVE_CONFIG_H -I. -I../..  -I/usr/include/glib-2.0 -I/usr/lib/x86_64-linux-gnu/glib-2.0/include -DGLIB_VERSION_MIN_REQUIRED=GLIB_VERSION_2_32 -pthread -I/usr/include/gtk-3.0 -I/usr/include/at-spi2-atk/2.0 -I/usr/include/at-spi-2.0 -I/usr/include/dbus-1.0 -I/usr/lib/x86_64-linux-gnu/dbus-1.0/include -I/usr/include/gtk-3.0 -I/usr/include/gio-unix-2.0/ -I/usr/include/mirclient -I/usr/include/mircommon -I/usr/include/mircookie -I/usr/include/cairo -I/usr/include/pango-1.0 -I/usr/include/harfbuzz -I/usr/include/pango-1.0 -I/usr/include/atk-1.0 -I/usr/include/cairo -I/usr/include/pixman-1 -I/usr/include/freetype2 -I/usr/include/libpng16 -I/usr/include/gdk-pixbuf-2.0 -I/usr/include/libpng16 -I/usr/include/glib-2.0 -I/usr/lib/x86_64-linux-gnu/glib-2.0/include -DGDK_VERSION_MIN_REQUIRED=GDK_VERSION_3_4 -pthread -I/usr/include/libnm -I/usr/include/glib-2.0 -I/usr/lib/x86_64-linux-gnu/glib-2.0/include -DNM_VERSION_MIN_REQUIRED=NM_VERSION_1_2 -DNM_VERSION_MAX_ALLOWED=NM_VERSION_1_2 -pthread -I/usr/include/libnma -I/usr/include/libnm -I/usr/include/glib-2.0 -I/usr/lib/x86_64-linux-gnu/glib-2.0/include -Wdate-time -D_FORTIFY_SOURCE=2 -I../../shared -I../../properties -DTEST_SRCDIR="\"/<<PKGBUILDDIR>>/properties/tests\"" -DTEST_BUILDDIR="\"/<<PKGBUILDDIR>>/properties/tests\"" -Wall -std=gnu89 -Wshadow -Wmissing-declarations -Wmissing-prototypes -Wdeclaration-after-statement -Wformat-security -Wfloat-equal -Wno-unused-parameter -Wno-sign-compare -fno-strict-aliasing -Wno-unused-but-set-variable -Wundef -Wimplicit-function-declaration -Wpointer-arith -Winit-self -Wmissing-include-dirs -Wno-pragmas -g -O2 -fdebug-prefix-map=/<<PKGBUILDDIR>>=. -fstack-protector-strong -Wformat -Werror=format-security -Warray-bounds -Wunused-value -c -o test_import_export-test-import-export.o `test -f 'test-import-export.c' || echo './'`test-import-export.c
/bin/bash ../../libtool  --tag=CC   --mode=link gcc -I../../shared -I../../properties -DTEST_SRCDIR="\"/<<PKGBUILDDIR>>/properties/tests\"" -DTEST_BUILDDIR="\"/<<PKGBUILDDIR>>/properties/tests\"" -Wall -std=gnu89 -Wshadow -Wmissing-declarations -Wmissing-prototypes -Wdeclaration-after-statement -Wformat-security -Wfloat-equal -Wno-unused-parameter -Wno-sign-compare -fno-strict-aliasing -Wno-unused-but-set-variable -Wundef -Wimplicit-function-declaration -Wpointer-arith -Winit-self -Wmissing-include-dirs -Wno-pragmas -g -O2 -fdebug-prefix-map=/<<PKGBUILDDIR>>=. -fstack-protector-strong -Wformat -Werror=format-security -Warray-bounds -Wunused-value  -Wl,-Bsymbolic-functions -Wl,-z,relro -o test-import-export test_import_export-test-import-export.o  -lgtk-3 -lgdk-3 -lpangocairo-1.0 -lpango-1.0 -latk-1.0 -lcairo-gobject -lcairo -lgdk_pixbuf-2.0 -lgio-2.0 -lgobject-2.0 -lglib-2.0 -lnm -lgio-2.0 -lgobject-2.0 -lglib-2.0 -lnma -lnm -lgio-2.0 -lgobject-2.0 -lglib-2.0 -ldl ../../properties/libnm-vpn-plugin-openvpn-test.la 
libtool: link: gcc -I../../shared -I../../properties -DTEST_SRCDIR=\"/<<PKGBUILDDIR>>/properties/tests\" -DTEST_BUILDDIR=\"/<<PKGBUILDDIR>>/properties/tests\" -Wall -std=gnu89 -Wshadow -Wmissing-declarations -Wmissing-prototypes -Wdeclaration-after-statement -Wformat-security -Wfloat-equal -Wno-unused-parameter -Wno-sign-compare -fno-strict-aliasing -Wno-unused-but-set-variable -Wundef -Wimplicit-function-declaration -Wpointer-arith -Winit-self -Wmissing-include-dirs -Wno-pragmas -g -O2 -fdebug-prefix-map=/<<PKGBUILDDIR>>=. -fstack-protector-strong -Wformat -Werror=format-security -Warray-bounds -Wunused-value -Wl,-Bsymbolic-functions -Wl,-z -Wl,relro -o test-import-export test_import_export-test-import-export.o  -lgtk-3 -lgdk-3 -lpangocairo-1.0 -lpango-1.0 -latk-1.0 -lcairo-gobject -lcairo -lgdk_pixbuf-2.0 -lnma -ldl ../../properties/.libs/libnm-vpn-plugin-openvpn-test.a -lnm -lgio-2.0 -lgobject-2.0 -lglib-2.0 -pthread
/usr/bin/ld: ../../properties/.libs/libnm-vpn-plugin-openvpn-test.a(libnm_vpn_plugin_openvpn_test_la-nm-vpn-plugin-utils.o): undefined reference to symbol 'dlclose@@GLIBC_2.2.5'
/usr/lib/gcc/x86_64-linux-gnu/6/../../../x86_64-linux-gnu/libdl.so: error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status
Makefile:691: recipe for target 'test-import-export' failed
make[5]: *** [test-import-export] Error 1
make[5]: Leaving directory '/<<PKGBUILDDIR>>/properties/tests'
Makefile:769: recipe for target 'all-recursive' failed


Maybe this is what you saw when you tried to compile 1.2.6 today? When did this last build on yakkety for you, because maybe there's a serious regression caused by another package?