latex packages should not depend on app-tex/tetex especifically. I think virtual/tetex should be the dependency. Thanks, Andrés Reproducible: Always
I don't see dev-tex/latex-beamer-3.07-r1 anywhere. 3.07 depends on || ( dev-texlive/texlive-latex >=app-text/tetex-3.0 ), what's your trouble with that?
The offending package is dev-tex/pgf. It has additional dependencies (dev-texlive/texlive-latexrecommended, dev-texlive/texlive-latexrecommended) that are unstable. Because of that tetex package is used. If you set keywords for these packages you can dump old tetex package.