I have one minor thing that bugs me about the interface: say you are dragging a piece around with left mouse-button, ready to move...at this point the potential squares that the piece can move are graphically highlighted as usual. If you right click at this point to cancel the move, however, the piece still stays selected and the potential squares are still highlighted so if you click one of them the piece will move. On top of this, the right click will still produce a circle (like of the arrow for spectators \ planning variety) on the right-clicked square.
In my opinion, the right click in this case should completely cancel the move and unselect the piece (kind of a complete reset to reconsider) since it is really easy to accidentally click a square not realizing the piece is still selected, but not dragged around with the mouse, also the arrow/circle highlighting shouldn't happen because the right click is only for canceling the piece selection (no one is trying to multitask drawing arrows / circles while also dragging pieces around). I find myself repeatedly accidentally moving pieces because of this and it is not the way it works in the live 2pc (if you mouse-down drag a piece there, right click to cancel the move, then try clicking on a potential square for the piece to move, nothing happens, the whole move sequence\piece selectionis canceled), I've also talked to some other people playing spell chess that said they have accidentally made moves because of this.
Currently what you need to do to completely cancel a piece being dragged around ready to move is right click to stop dragging it, then carefully click the board on a neutral square where that piece can't move to get rid of the highlighting for its potential squares; this feels very cumbersome and illogical. Also the right click while dragging a piece around should be completely reserved for canceling the move, and not also produce square highlighting at the same time.