Synced yesterday on x86, got the following block: --8><-- # emerge -D world [...] [ebuild NS ] net-misc/unison-2.27.57-r1 USE="gtk ocamlopt -debug -doc -static -threads" [...] [blocks B ] net-misc/unison:0 (is blocking net-misc/unison-2.27.57-r1) --><8--
How many versions of unison are installed? Unmerging unison and then re-emerging should fix this problem. It's certainly no bug - the ebuild has this feature to make sure no two conflicting versions of the same packages are installed at the same time.
Just the previous stable one, unison-2.13.16. What bothers me is the hint to unison:0. However, as you mentioned uninstalling it (emerge -C unison:0 in this case) fixed that, now I only have the known lablgtk problem left to fix...