If you bitbake something (say, tremor), then delete the build directory and bitbake it again, it installs entirely from sstate as expected. However, in this example, subversion-native and all of it's dependencies will also be pulled in via the magic dependency on subversion-native triggered via the SRC_URI being a svn: URI. This dependency is on the do_fetch task however and shouldn't be considered when installing from sstate as do_fetch was never executed.
http://git.yoctoproject.org/cgit.cgi/poky/commit/?id=5003d147617eed64532f2d7f7d12689622f99723
Verified in local sstate; not reproducible on master: 2cd061a29a94fdcdfec86732e6bcbb71c12c4afc Only do_populate_sysroot_setscene ran for subversion-native-1.9.2-r0