I don't understand why there would be file collisions since portage shows this version as "NEW" and "SLOTTED", but it does:
* * Searching all installed packages for file collisions... * * Press Ctrl-C to Stop * * dev-scheme/guile-2.0.11:12::gentoo * /usr/lib64/guile/2.0/ccache/rnrs.go * /usr/lib64/guile/2.0/ccache/statprof.go * /usr/lib64/guile/2.0/ccache/system/base/ck.go * /usr/lib64/guile/2.0/ccache/system/base/compile.go * /usr/lib64/guile/2.0/ccache/system/base/lalr.go * /usr/lib64/guile/2.0/ccache/system/base/language.go * /usr/lib64/guile/2.0/ccache/system/base/message.go * /usr/lib64/guile/2.0/ccache/system/base/pmatch.go * /usr/lib64/guile/2.0/ccache/system/base/syntax.go * /usr/lib64/guile/2.0/ccache/system/base/target.go * /usr/lib64/guile/2.0/ccache/system/base/types.go * /usr/lib64/guile/2.0/ccache/system/foreign.go * /usr/lib64/guile/2.0/ccache/system/vm/program.go * /usr/lib64/guile/2.0/ccache/system/xref.go * /usr/lib64/guile/2.0/ccache/texinfo.go * /usr/lib64/libguile-2.0.la * /usr/lib64/libguile-2.0.so.22.7.2 * /usr/lib64/libguilereadline-v-18.la * /usr/lib64/libguilereadline-v-18.so.18.0.0 * /usr/lib64/pkgconfig/guile-2.0.pc * * Package 'dev-scheme/guile-2.0.11-r1' NOT merged due to file * collisions. If necessary, refer to your elog messages for the whole * content of the above message.