Latest Beta 3 - appears to have lost contact with in-built images

[Phuket2]

Was not sure were to report this. Here or on Github. Anyway, I choose here.
But the following has stopped working
btn.image=ui.Image.named('iob:arrow_down_a_256')
Even in the editor, the pop up icon is just white. Can see the images are still there, something pointing the wrong way I guess

[omz]

Thanks, I'll look into it, I've moved a lot of things around in the last build...