VTP pruning enabled, but can still see broadcasts

hi all,

I'm trying to lab the VTP prunning cmd in GNS3. what i'm having trouble with is after enabling vtp prunning, wirehsark can still see broadcast packets in links that shouldn't have.

my setup is simple:
Sw1----Sw2----Sw3
vtp mode server
vtp domain bob
vtp prunning
vlan 12
vlan 23
all VLANs propagate all good.

on Sw1:
int vlan 12 with addr 12.12.12.1/24

on Sw2:
int vlan 12 with addr 12.12.12.2/24
int vlan 23 with addr 23.23.23.2/24

on Sw3
int vlan 23 with addr 23.23.23.3/24



my understanding is with vtp prunning, vlan 12 flooded traffic should only be on Sw 1 & 2, and vlan 23's should only be on Sw 2 & 3.

but from Sw1, when I ping 12.12.12.99 (which should ARP broadcast in vlan 12 only), wireshark can still see those broadcasts between Sw 2 & 3.

and if I run no vtp prunning, and ping again, I see the exact same ARP broadcasts between Sw 2 & 3.

so I don't know what's changed running vtp prunning or not, except under show int trunk the pruned list of Vlans seem to change.

What's going on??

Thanks for reading.