guacamole-server has optional deps on net-libs/libssh2, net-misc/freerdp, net-libs/vncserver, media-sound/pulseaudio, and media-libs/libvorbis. However, it does not enable/disable the corresponding features via configure flags or other means. These deps are therefore "automagic": the package will link with these libraries if they happen to be installed, regardless of the user's USE setting. http://wiki.gentoo.org/wiki/Project:Quality_Assurance/Automagic_dependencies On a related note, the detection logic for freerdp appears to be flawed and rdp support is silently disabled when building against net-misc/freerdp-9999.1.
Thanks Mike, this is fixed in the 0.9.3 version. For freerdp i just depend on a lower version for now...