All attack/defence skills have 10% added to them when a character is confident. However, if melee or ranged defence is negative (e.g. for a wildman or a cocky character), 10% of this is a negative value, and so that amount is actually deducted from their defence!
I’ve noticed a similar thing in the past with the dodge bonus. If a character has more max fatigue than initiative, and uses lots of skills so that initiative goes negative, the 15% dodge bonus is a negative value that’s deducted from defence skills!
Presumably, the same thing would happen with the Lone Wolf +10% bonuses and any other such bonus based on a percentage.