A Locked Gauntlet provides a +10 bonus on CMD checks against all disarm attempts, regardless of source. But this means the gauntlet only protects you against disarm attempts done against you, not your own failed disarm attempts. For that, you must have some ability to prevent you from being disarmed.
For example, gauntlets and spiked gauntlets (normally) cannot be disarmed. Weapons with the Attached quality (from Weapon Master Handbook) also cannot be disarmed.
Regardless, while it is difficult to disarm an opponent wearing a weapon locked by a locked gauntlet, it is not impossible. Failing by 10+ means you did something horribly wrong, like twisting your arm in a wrong way and being disarmed as consequence.
That said, it makes perfect sense that you can still disarm yourself for failing a disarm check, as the weapon isn't really attached to your hand, but simply being locked in a position that makes disarming it difficult. When you are trying to disarm your enemy, you are moving your weapon in ways to force her to drop her weapon, and thus the gauntlet is no longer helping you there.
If I may suggest advice, a weapon cord is much more helpful in that situation.
However, there are two instances in the rules claiming that you items held by a locked gauntlet cannot be dropped. Both are cases of specific rules that override a more general rule. First on the Arm Targeting Hit deed from the Gunslinger class:
Arms: On a hit, the target takes no damage from the hit but drops one carried item of the gunslinger’s choice, even if the item is wielded with two hands. Items held in a locked gauntlet are not dropped on a hit.
And second on the Burning Disarm spell:
Circumstances that prevent the creature from dropping the item (such as a locked gauntlet) mean the creature gets no saving throw.
This makes me believe that the rules-as-intended is for a locked gauntlet also help against you dropping the item yourself, while making it harder for others to force the item out of your hands, either by disarming, shooting at your arms, or making your weapon burn out of your hands.
Fun fact: From the rules-as-written, the Locked Gauntlet had to say something about either that it works as a gauntlet or mention that it cannot be disarmed as well. But common sense would hit you hard on the head if you rule that a gauntlet could not be disarmed but a locked gauntlet could.