I've now fixed the HUD texture-update-problem. One part was fixed by Yuri's moving the update-Appearance call to FrustumCuller. I think it is due to Shader-State-cache. The other part is fixed by retraversing the scenegraph even if parallely projected, after a NodeComponent was changed. So you seem to be right in this point, too, Yuri
There's a last point that needs to be fixed. Some Labels show the left part of the text without the background. I hope this is fixed by bohdan's transparency-sorting patch. If not, I'll investigate.