I have two overlays enabled for bigboard. I noticed that the up and down arrows don't always work as expected. Pushing the down arrow on the top one pretty much always toggled their position. But doing something like pushing the down arrow on the bottom one then it's up arrow will cause it to be reordered with the other OL layers (Annotations & Participants) which can be seen by enabling the layer switcher.
I have two overlays enabled for bigboard. I noticed that the up and down arrows don't always work as expected. Pushing the down arrow on the top one pretty much always toggled their position. But doing something like pushing the down arrow on the bottom one then it's up arrow will cause it to be reordered with the other OL layers (Annotations & Participants) which can be seen by enabling the layer switcher.