As mono-2.0 was released 6.10.2008, libgdiplus-2.0 was released too. mono-2.0 (bug #240289) might depend on this. dev-dotnet/libgdiplus-2.0 compiles well with simply renamed libgdiplus-1.9.ebuild. They released "pre_2.0" -versions named as "2.0" which confuses emerge if someone made own ebuilds. It seems, that contents have changed since then.
Masked in tree now. We're waiting for the full range of packages to get in before we unmask.