The text of Concentration Aura and Improved Concentration Aura has always puzzled me.

For concentration aura the text reads:-

"Gives a 35% chance of ignoring spell interruption when damaged to all party members within 30 yards. Players may only have one Aura on them per Paladin at any one time."

For 3/3 Improved concentration aura the text reads:-

"Increases the effect of your Concentration Aura by an additional 15% and gives all group members affected by the aura an additional 15% chance to resist Silence and Interrupt effects."

The reason this puzzled me is that in the defination of improved concentration aura, it first says increases the effect of concentration aura by 15% (concentration aura's effect being to avoid spell interruptions) and then states at the end an additional 15% to resist Interrupt effects. This always seemed like repetition to me and badly worded.

However earlier i had a look at thottbot's definition of these two abilities. For improved concentration aura, the spell is here:-

http://www.thottbot.com/?sp=20256

It's effect is to increase the effects of Concentration Aura by 15% (which i presumed would be a resist interrupt and resist silence effect)

However, looking at concentration aura, it infact has 3 effects, listed here:-

http://www.thottbot.com/?sp=19746

The effects being
1) Resist Spellcasting Delay (Value:35)
2) Resist Silence (No Value, which i presumes means 0)
3) Resist Root / Snare (No Value, which i presumes means 0)

This would mean that when improved concentration aura was applied to it, it would increase the resist spellcasting delay to 50, resist silence to 15, and also resist root / snare to 15.

Am i right in saying then that improved concentration aura gives a resistance to root/snare effects (something i never knew before), and that there is a typo in the improved concentration text, when it should be reading something like this:-

"Increases the effect of your Concentration Aura by an additional 15% and gives all group members affected by the aura an additional 15% chance to resist Silence and Root/Snare effects."

Taking a look at the affected spells for the "Apply Area Aura: Mod Mechanic Resistance (Root/Snare?)" I think it's more likely that that Aura is resistance to spell-school lockout. Curious why Kick isn't in the list, though.

The significant part of that "root/snare" bit is, in fact, the question mark. Thott doesn't know what it is, but if you check the affected spell list, it's pretty clear: the affected spells (mostly counterspell, but a few others) are those with 'interrupt' effects, not snare/root effects.
When the description says "interrupt effects" it means abilities (like kick/pummell/earth shock/counterspell) which do nothing if the target is not casting a spell, but will interrupt any one in the process of being cast, usually with an accompanied short term lock on the school - these are distinct from both silence effects and the casting delay on damage, and this is why they are listed separately in both the description and the spell data on thott.

So the tooltips should read as follows?

Concentration aura:
"Gives all party members withing 30 yards a 35% increased chance of ignoring casting time delays caused by damage. Players may only have one Aura on them per Paladin at any one time."

3/3 Improved concentration aura:
"Increases the effect of your Concentration Aura on casting time delay by an additional 15% and gives all group members affected by the aura an additional 15% chance to resist Silence and Interrupt effects."

'Spell interruption when damaged' is the same thing as 'casting time delays caused by damage'
It's just the way blizzard words it; and since the unimproved tooltip only mentions these spell interruptions when damaged as concentration aura effects there is no need, grammatically, to reiterate it, save for clarification. 'the effect of your concentration aura' refers to the only effect listed on the unimproved tooltip.
Might be a bit obscure but in practice that is the way I would expect it to work without trying to read to much into the tooltips.

As far as the root/snare, I would imagine thottbot doesnt have em all listed. For example that web/root the spiders in stratholme cast also prevents spellcasting, makes me wonder if improved concentration would let you resist it.

edit: looked up aforementioned web: http://www.thottbot.com/?sp=15471
It appears to me imp concentration aura would work indeed.

For the Basic Concentration Aura, the 2nd and 3rd entries are just placeholders. As said above, "Resist Root / Snare?" is actually "Resist Spell Cast Interrupt (and the attached lockout effect). The "Resist Root/Snare?" is either just a guess or something wrong in the "local spell effects list".

Blizzard should rip you off and replace the tooltips with those, they describe the effects correctly.