Put the summary of the bug you're having here
The block of the (diamond) sword is bugged in f5 mode
What I expected to happen was...:
Just the normal block from the sword

What actually happened was...:
sort of half blocking, the sword was not in front of my chestplate but next to it

Steps to Reproduce:
1. grab a sword (I had a diamond one)
2. go into f5 mode (so you see your character from the front)
3. press right click