Suggestion: Can you move the collapse button to the left of the username? One way I tend to use nested comment threads is reading all top comments, collapsing as I go.
Since collapse persists on page loads, hopefully it is better now. Then again, we can un-vote now, so I think we're back to having the behavioral advantages and disadvantages being close enough that it's a toss-up what any particular user thinks is more of a problem.
yes. it doesn't make sense from any design perspective. alignment is an important visual signifier and usability design tool.
there is no reason why vote arrows would be aligned across posts (it suggests a connection where there is none), while there are several for the collapse buttons.
Great stuff, overall -- thanks!