Shieldbash and shield not calculating To Hit correctly

Description

Shieldbash and shield do not seem to be calculating To Hit correctly...

Shieldbash (Light) Melee; Number of Attacks: 1; Crit: 20; Crit Multiplier: x2; Reach: 5 ft. To Hit: +5 = +4[BAB] +4[STAT] +0[SIZE] -4[MAGIC] +1[MISC]
Damage: 1d3+4

What is the -4 magic from?

Then the shield itself comes out like this...

Shield +1 (Light/Steel/Mithral) Melee; Number of Attacks: 1; Crit: 20; Crit Multiplier: x2; Reach: 5 ft. To Hit: +4 = +4[BAB] +4[STAT] +0[SIZE]
Damage: 1d3+4

Only +4 to hit, but it clearly states a +4 and +4...