The original runtime had far, far worse GC pauses. They concentrated on making sure they could make a good one later rather than getting a perfect one out the door immediately. There was also a series of crashing bugs of varying severity in the first couple of versions. Even then you had to go a bit out of your way to find one, but they're a lot harder to come by now.
One of the advantages of not mutating the language too much is that there aren't very many things like this in the last few releases. I would expect the first 2.0 release to have a few rough edges even in the first non-beta release.
Nothing that surprising, really.
If you look at Go's release note history: https://golang.org/doc/devel/release.html look towards the first few releases for the bugs they mention. For instance, here's a 1.1 fix: https://github.com/golang/go/commit/d72c550f1c7e13c323f4507b...
One of the advantages of not mutating the language too much is that there aren't very many things like this in the last few releases. I would expect the first 2.0 release to have a few rough edges even in the first non-beta release.