I installed a new version of the mod and i still have the same issues as it was described here

Two-handed weapon display overlaps issue still remains

Apparently, you still can hold a katana in off-hand. I managed to do this by opening inventory menu, pick up the katana item, put it back and press F still being in the menu.

And the shield animation still doesn't displays, even though it's mentioned in changelog
(on this screenshot i hold right click and it seems that shield is working, as the player moves slower, but visually nothing changes)

I don't use any mods except OptiFine HD_U_G7

Normally, Katana and other two-handed weapons can't be put in offhand both clicking in Inventory and pressing the 'F' key. I don't know why you guys can put the katana in the offhand. Does the same thing happen when you uninstall the Optifine?

Plus, I found the shield animation is not played when the shield is held by offhand. It will be fixed in next update.

Here is a video of how i do it. You pick the icon up, put back again and press F.

And yes, you are right, I forgot to mention that shield doesn't work only in off-hand.

Ooh, I didn't know that it's possible to swap the item under the mouse pointer. Thanks for reporting and will be fixed in the next version.