ABout noting the Bold text.
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Flaming Burst
Upon command a flaming burst weapon deals +1d6 points of bonus fire damage on a successful hit. In addition it also explodes with flame upon striking a successful critical hit. The fire does not harm the hands that hold the weapon. Flaming burst weapons deal +1d10 points of bonus fire damage on a successful critical hit. If the weapon’s critical multiplier is x3, add +2d10 points of bonus fire damage instead, and if the multiplier is x4, add +3d10 points of bonus fire damage. Bows, crossbows, and slings so enchanted bestow the fire energy upon their ammunition.
Caster Level: 12th; Prerequisites: Craft Magic Arms and Armor and flame blade, flame strike, or fireball; Market Price: +2 bonus.
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And yes, the bonus damage stacks as it is not one of the bnous types (luck, moral, insight etc).
Of course, if it doesn't you can be an evil bastard DM who gives overpriced uneffective weapons to his PCs, so that they can't upgrade them as easily. Whatever floats you boat.