I've reproduced this several times. Apparently, dying as a werewolf and loading an earlier save will cause shield bashing to no longer stagger your opponents. Power attacks with all kinds of weapons are also affected. Here's what I did:

Become a werewolf if you're not one. Save. Transform with your shield equipped, attack someone a few times, then let them kill you, and load the save. You will no longer stagger people when shield bashing, which sort of defeats the whole concept.

Exiting to the main menu and loading the save from there fixes the problem, but it's still annoying. I'll try to test it some more and see if there's a specific condition that triggers it.

When I transformed to a warewolf with a shield equiped, I came out.. equiped my other stuff.. and then my shield turned towards me when I moved. Add to this that when I blocked I held it with both hands, I got confused.

I used to have problems with my weapons staying in my hand when I transformed. But I've never died in wolf form, the Dude is too fast to catch!

I used to have wolf-form weapon problems like you, than I took an arrow in the knee. Said screw it and restarted the system and it was fine.

I had that too, I wonder if it's related to pressing hotkeys in the delay between activating the power and actually transforming. I've also seen a guy chop wood using a two-handed sword that was stuck to his arm. I'm not sure if the bug occurs just at the transformation or if you have to die, but it's definitely the wolf form that's messing up the stagger.