fasttrack broken in 6.39rc62

Have a setup with LAN full of wired clients, an ubiquity AP that has a vlan1 interface and vlan11 interface (for guest access)
standard interface is bridged into LAN bridge

/interface bridge
add fast-forward=no name=Bridge-LAN
add fast-forward=no name=GuestWLANBridge

/interface ethernet
set [ find default-name=ether1 ] mac-address=name=“ETH1 - Internet”
set [ find default-name=ether2 ] name=“ETH2 - Ubiquity”

/interface vlan
add interface=“ETH2 - Ubiquity” name=“VLAN 11 - Guest” vlan-id=11
/interface bridge port
add bridge=Bridge-LAN interface=“ETH2 - Ubiquity”
add bridge=GuestWLANBridge interface=“VLAN 11 - Guest”

Have standard fasttrack rules setup and quite standard firewall rules setup

add action=fasttrack-connection chain=forward comment=“defconf: fasttrack” connection-state=established,related
add action=accept chain=forward comment=“defconf: accept established,related” connection-state=established,related

All was working OK until updated to 6.39rc62 (to fix switch hang issue when port flapping).
Now suddenly all wireless clients report their internet access is not working (or is super slow). All clients connected directly to MT via LAN work OK.
Disabling fasttrack rule resolves the problem, so fasttrack got broken somewhere in the way.
Any ideas, or it is a bug?

Reproed this on another device also 6.39rc62.
Setup is this:
[VM]-[CHR]-[MT-6.39rc62]-[Internet]

When fasttrack is on, the VM has issues accessing the net. Disabling fasttrack resolves issue. Worked with previous version.

machines connected directly to MT in question (via lan or wireless) experience no problem

Downgrading to 6.39rc60 fixes the problem, so something new in 6.39rc62 by the looks of it :S