advanced home DIY-er here. I put in a new Murray (Siemens) AFCI breaker and new 14-2 wire from the breaker box up straight to a light in a bathroom I'm remodeling (single wire for the complete run).
If I disconnect the load and neutral from the fixture (so they're hanging down, exposed), and turn on the breaker, all is fine. It stays powered up.
If put an LED bulb in a $2 plastic basement-style "outlet box lamp holder" and connect the load and neutral to it and throw on the breaker on again, it immediately trips the breaker. Neither the arc-fault or ground-fault LED indicators light up on the breaker. I believe this indicates an over-load protection, which seems odd for a 10w bulb.
so no load = no trip 10w bulb directly connected = trip
note: I pulled 3 other lines up with this one and they all work fine on the traditional breakers they're connected to. We did have blown-in insulation installed that meant guys drilling a million holes in the side of the house, potentially where that wire is. The likelyhood of partially damaging one wire (and not reporting it) but not severing it, or damaging any of the other circuits doesn't seem very high to me.