The main difference between betza.js and betzaNew.js is that the latter checks the legality of the moves that it highlights, and marks the illegal ones with a grey cross. With betza.js all pseudo-legal moves are highlighted.
It appears that swap with your own King is considered illegal, and when performed (the Diagram does not prevent that), it does not lead to a swap, but to the reverse King move. There obviously is a bug there, and I will look into it.
The main difference between betza.js and betzaNew.js is that the latter checks the legality of the moves that it highlights, and marks the illegal ones with a grey cross. With betza.js all pseudo-legal moves are highlighted.
It appears that swap with your own King is considered illegal, and when performed (the Diagram does not prevent that), it does not lead to a swap, but to the reverse King move. There obviously is a bug there, and I will look into it.