The description for Battle Cleric's Lore says "You gain a +2 shield bonus to AC", but shield bonuses are a special type of bonus that boosts AC and Reflex. Is this an exception, or can I boost Reflex too even though it only mentions AC (in Dragon #400)?
In DnD4 the rules are very strict. If it says AC, you only increase AC, even if something implies it otherwise.
So you do not get any bonus to Reflex.
You can't boost reflexes too, but it's not an exception.
Shields are items that add a shield bonus to AC and a shield bonus to Reflexes. This does not mean that everything that gives a shield bonus to one of the two needs to give a shield bonus to the other: it's coincidental.
Battle Cleric's Lore only gives a shield bonus to AC (arguably because it's not a shield, but that's just because we'd expect any shield to get both, not because it's universally true).