Really though, this happens all the time in the game. Objects that shimmer which can't be looted. Just more bugs.
This is exactly it. In the Prologue alone, if you bother plundering all the houses before infiltrating the monastery, there are plenty of loot containers that shine up, but due to the positioning of various obstacles and what, you can't reach them. As far as I can tell, all of these just contain 'random' loot anyway, so it's not like we're missing out on something important.
As for the Poisoned Zerrikanian Saberra, it hangs above her fireplace, but only at the very end of Chapter 2, and only if you went with Iorveth in Chapter 1.