Take for example glibc which has lazy bindings for a setuid binary so it fails with FEATURES="stricter". I usually use ebuild glibc-2.4-r1 merge with FEATURES="-stricter" if a package fails like this so I do not have to compile it again. In this case portage runs src_install again which is really not needed because the end result should be the same as with FEATURES="stricter". With normal packages this is not a big problem but the src_install of glibc takes quite long.
This is fixed in svn r2832 for release in 2.1_pre7.
Pardon, it should be fixed in 2.1_pre6. Install phase qa checks were moved out of ebuild.sh.