Put the summary of the bug you're having here
1st "mini" bug : Upon logging in any of the (four so far) snapshots for 1.9, adding attributes (such as +attack damage, or +speed, when holding/using/equipping an item) is broken. For example: if a sword gives speed upon equipping, it will have a very long description on where it affects: when in offhand: when in main-hand: and so on. This isn't really a bug, but it does need to be changed because it fills half the screen with pointless information: in command blocks there should be a tag that allows editing of what "space" the item must be equipped in order to use the attributes (for example, an item that gives speed can only give speed if it is in ___ slot, or off hand slot ex.)

Real bug: When using an item with an attribute in offhand, it will not always give the attribute to the player, unlike main hand which always works.

What I expected to happen was...:
Describe what you thought should happen here

The item in the offhand should always give the attribute, and if it has similar attributes to the main-hand, they should stack (if they both increase attack damage by +1, together they should be +2)

What actually happened was...:
Describe what happened here

They would both work at the same time at first, but then after switching around, only main hand would provide the attribute (better explained below)

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ... First begin by getting two swords (it can be anything, use sword for this example) and use command blocks to add any attribute to it, in this case we will add +max health 1 to both of them.
3. ... Now put one in your offhand, and one in your HOT BAR, BUT DO NOT HOLD IT YET
4. ... On screen, (if you are in survival) you should now have extra HP.
5. ... now hold the 2nd, duplicated sword in your MAIN hand. (you should be duel wielding now)
6. ... you still have the same, unstacked stats (which in the first paragraph of this bug report, I suggested should stack)

7. ... Now, scroll over to a different slot in your hotbar so you are only holding the sword in OFFHAND.

8. ... If you didn't notice, you now no longer have the stats.

9. ... Scroll back over to your main-hand sword, and they return.

It seems like the offhand sword doesn't register unless doing step 10:

10. ... replace the sword in your offhand by clicking it out, and then putting it back in --> the stats should reappear now.

I am no master at java coding or anything like that, but I believe the problem is with how attributes are identified in held items: perhaps making it so we can choose where items must be held to activate the modifiers and attributes, and/or put a limit on where it can be held.

The below pictures display in order:
1: the sword and its attributes.
2: the offhand sword not working