Not sure if this is a bug or expected behaviour, but when you create a TreeList with micro=true, the expanderFirst parameter does not work.

Code:
<TreeList store={this.store} ui="nav" micro={false} expanderFirst={true}/>
Work as it should.

Code:
<TreeList store={this.store} ui="nav" micro={true} expanderFirst={true}/>
Does not work, expander is still last.