I am using Iron Backpack version 1.1.1 on MC 1.7.10 and when you turn your character to the left or right, you can see the backpack in your FOV. Included is a pic explaining further.
http://imgur.com/I3JYm5g

Is it only when you spin rapidly to either side? Because, if so, it is working as intended (since, in real life, if you turn quickly the backpack takes a moment to "catch up" and so you see it for a moment before it goes back behind you). It should go away soon after you stop spinning though.

If that isn't the case though:

• What is your field of vision setting at?
• What version of IB are you on? You provided one that doesn't exist. If you aren't on at least version 27/1.2.9 please update and let me know if it happens again.

Sorry. I put version of a different mod here. I was using 1.2.10. My FOV is set to normal. I will download the latest version today, which is 1.2.11 and let you know.

That won't change anything, I didn't mess with the rendering in the last version.

Can you answer this question please:

Is it only when you spin rapidly to either side?

Alright, seems to be no other issues from other people, so I am closing this, I think it is working as intended.