You can also use 'bool' in your ip sla and use several IP's to monitor with and/or. Check this link out: http://packetpushers.net/using-ip-sla-delay-feature-to-safely-monitor-lossy-links/
That is because when you use subinterface you trunk the switch. Vlan 1 is the native and by configuring the physical interface that causes the asa to pass untagged traffic. Never use Vlan 1 and always change native Vlan on uplinks.
