I have a few TL-SG3428MP switches.  Some of them are hardware v2, others are v5.  My problem is that on ALL of the v5 switches, the Voice VLAN feature does not appear to work.  All are on the latest firmware.

They are configured as follows: each switch has a LAG back to the main switch.  The LAG is untagged on VLAN1 and tagged on VLAN20 (phones). Voice VLAN is enabled on all ports.  OUI for the phones is present. I have the v5 switches configured identically to the v2 switches as far as I can tell.

On the v5 switches, the phone ends up on VLAN 1. The log indicates the phone was detected and is being put into VLAN 20.  But it actually ends up on VLAN 1.  If I change the PVID of the port a phone is connected to VLAN 20, it works, but that defeats the purpose of the Voice VLAN feature.

On the v2 switches, I get the expected behavior; the device ends up on VLAN 20 and works correctly.

I have tried resetting one of the v5 switches to factory defaults and enabling Voice VLAN again.  I get the same result; it simply does not work.

If it matters, the main switch these are connected to is a TL-SG3452P.  Voice VLAN is also enabled on that switch, and it works as expected.

Any ideas?  Is there something I could possibly be missing?