rhino-1.5_rc5 is an ebuild for rhino 1.5R5, whose 'R' means 'release'. Thus, the ebuild should simply have the version 1.5.5 instead of abusing _rc for release. I suggest it because I see rhino 1.6R1 release candidate 2 on its web site. It can be rhino-1.6.1_rc2 but not rhino-1.6_rc1_rc2. Reproducible: Didn't try Steps to Reproduce:
fixed :)