From the 3E Main FAQ:
If you use the true strike spell and you get a threat, does
the +20 bonus from the apply to the critical confirmation
roll? Would the +20 bonus apply to the extra attacks you
get from the Cleave, Great Cleave, or Whirlwind attack
feats?
When you roll to confirm a critical, you use whatever
bonuses applied to the attack roll that made the threat, no
matter where those bonuses came from.
True strike affects only one attack. (Rolling to confirm a
critical is not a separate attack for this purpose.) If you make
multiple attacks in a round, your bonus from true strike applies
only to the first attack you make, no matter how you managed
to get multiple attacks.
In the Cleave feat, the phrase "at the same bonus" distinguishes it from other feats which grant an extra attack "at your highest base attack bonus".
If you have a BAB of +6/+1, and you drop an opponent with your first attack, then the Cleave is calculated using the +6 and any applicable modifiers. If you drop an opponent with your second attack, then the Cleave is calculated using the +1 and any applicable modifiers.
Since True Strike discharges on your first attack, it is not an applicable modifier to the Cleave attack.
Likewise, if I am Paladin making a mounted charge and Smiting Evil at a hobgoblin with my Goblinbane sword, then I have:
+6: BAB
+2: Strength bonus
+2: Charging
+4: Smite Evil
+1: Enhancement bonus
+2: Bane bonus
+1: Higher Ground bonus
Total: +18.
I hit easily, of course, drop the hobgoblin, and Cleave into his Dire Wolf companion.
I'm no longer charging. The wolf isn't evil, nor is it a goblinoid. And since it's Large, I don't get the higher ground modifier.
So, using the same BAB figure (+6), I add any applicable modifiers - my Strength bonus (+2), and the Enhancement bonus of my sword (+1), for a total attack bonus of +9.
If I'd gone the other way, charging the wolf and using Smite Evil on the Cleave of the hobgoblin instead, then my bonus would have been +11 on the initial attack, and +16 on the Cleave.
The feat text, to remove ambiguity, should say "at the same base attack bonus". It doesn't, but that's how it works.
-Hyp.