I noticed that even upgrading to latest version of autounmask (0.21 on my portage tree) I got the same loop bug of the previous versions.
Exactly like for the previous version the problem regards an infinite loop generating when unmasking a package and it’s caused by not understanding the PortageXS function getArch(). To avoid the problem and using this wonderful tool without PortageXS it’s possible to manually set the arch on the bin file.
Just open it with your favorite editor as Root
Then find this line
my $arch = $pxs->getArch();
comment it and add this other
my $arch = 'amd64';
obviously replacing amd64 with your arch.