That looks like a bug to me - not intentional.
If something doesn't look right, it probably isn't. The way editors are loaded is completely different now, so this is probably a side effect of that.
Talked to the developer, and as expected there's a lot going on behind the scenes that's causing this. Not that it matters to you or that you care WHY it's not working right.
The minimum expectation is that you should be able to resize the columns. We'll get there!
Fixed. Will be available next release.Parent/child tables are now sized and scrolled independently and columns are resizable.