When I am using instances (Fast), and preview render, whenever I make change to material parameter, instances are lost, I need to hit Render to be able to see them again. This was working nice in H11 as I recall.

Can someone confirm this?

Is it possible that no one have this problem? It is happening for me all the time, even with latest stable release.
If I use Render Preview almost any change makes instances disappear in render until I hit Render again.

Am I doing something wrong here?

http://screencast.com/t/xNeFWgyM [screencast.com]

This is a bug, already logged (46800 and 48164). It's related to IPR only.