frame.js putmsg not expanding @-codes

I'm creating a popup window using the following:

        const popup = new Frame(
                frame.x + 1,
                Math.floor((frame.y + frame.height - 13) / 2),
                frame.width - 2,
                13,
                BG_BLUE|WHITE,
                frame
        );

Now, when I write something with @-codes, it appears verbatim and isn't processed.

popup.putmsg("This node is @NODE@");

for example, puts "This node is @NODE@"