I think my installation (and reinstallation) is getting corrupted, or that Steam is somehow not fully upgrading me to 1.7. OR they have a bug thats unique to some Windows 7 configs, but not others. I am not the only person affected - I know two people with the exact same problem, yet I also know several others for whom it works perfectly.

I'm 99.99999% positive this is NOT Mod-related. I have no mods installed currently, and when I encountered the bug, I comnpletely uninstalled skyrim and performed a fully-clean reinstall via Steam, (after deleting all folders) with no mods whatsoever. No change - the bug is still there.

What's specifically happening is that native ObjectReference.AddItem() and Actor.AddItem() are no longer supporting FormLists, and they throw an error when you try to. This did not happen prior to 1.6.

This bug is most obvious when you try to loot a Salmon Activator - Prior to 1.7, we used to get meat, now we get an error message. Whats supposed to happen here is that additem adds one of each items in the formlist to the container, but instead it throws the following error:

[08/12/2012 - 05:30:50PM] error: (0010EE1E): cannot be put in a container.
stack:
[ (00000014)].ObjectReference.AddItem() - "" Line ?
[ (FF000BE5)].critterFish.OnActivate() - "Critter.psc" Line 137

...where 0010EE1E is the standard Salmon treasure Formlist.

I'd appreciate if someone can verify this problem, and suggest a solution. I'd hate to think that I'm writing mods against a corrupted or outdated exe/bin/war/jar/dll or whatever is broken here...

I can verify. The first salmon I tried to catch just now (off a new game with no mods outside LAL loaded) gave me nothing and after checking the Papyrus logs, that error was there. All other salmon afterwards actually did work, though. It was only the first call that failed.

Since I can pretty much confirm this is a vanilla bug, I've posted it to the USKP team.