Do you use wxGTK 2.4.1 or 2.4.2? Try emerging 2.4.2, that's what I use (since you probably don't want to set ACCEPT_KEYWORDS [that would try to upgrade too much unrelated things], do a emerge -u /usr/portage/x11-libs/wxGTK/wxGTK-2.4.2.ebuild which will only upgrade wxGTK).