The bug
In first person mode you will only block with your main hand shield, but in third person mode you will block with both. Though I think it isn't needed
How to reproduce
Video demonstrating the issue: https://www.youtube.com/watch?v=a6rJKS9DR6o
Code analysis
Code analysis by @unknown can be found in this comment.
Linked issues
is duplicated by 28
relates to 2
Comments 20
Will you please look at my bug report, too? It was marked as a duplicate of this, but it is much more informative and also tells bugs about dual wielding with other items such as bows, tools, and eyes of enders.
confirmed, but only when both are occupied by a sword