disallow setting RNA attributes while drawing, this is bad practice so enforcing here has the benifit of making sure people are not manipulating blender scene data in a drawing panel for eg.
This is ifdef'd and may be disabled later on, or only enabled in debug mode.
This applies to setting any RNA value that has an ID and is not a screen or window-manager datablock.
Some addons break this rule and need fixing but from my tests blender UI scripts are ok. [sic]
This breaks LuxBlend25 and a few other scripts, I don't how hard it would be to fix. My current solution is to just revert the change and recompile.