Error when changing material on instanced mesh when isVisible set to false

Hi all,

I have this playground:

http://www.babylonjs-playground.com/#V3N96R

In it, there is box, and an instance of box, which is box2. box has isVisible set to false, and after 1000 ms, has its material changed to swapMat. This is what happens then:

Chrome/Opera: When swapMat is normalMat, nothing seems to happen. When swapMat is set to greenMat, box2 disappears, and the following errors show:

Firefox/Edge: When swapMat is normalMat, box2 turns white. When swapMat is greenMat, box2 turns green with no errors.

Setting isVisible to true right before/after changing the material makes it work as expected.

The same happens in the stable version.

What could it be?  Thanks.