Gadgets don't show on hidden/shown canvas

I'm creating a window with the WINDOW_HIDDEN flag, or hiding it straight after creation.

Then attaching a canvas to it, and some gadget to the canvas.

When using 'showgadget' to reveal the window, some of the gadgets are invisible - textfields and canvases don't show - buttons do.

This problem also arises when attaching gadgets to a hidden canvas, then revealing the canvas, also with 'showgadget'.

Any ideas how I might remedy this?

Apologies if I'm missing something obvious.

OK - I think I've sorted it. Neglected to flip the canvas. Silly me.