No I mean do not touch the configuration (leave smlt enabled on MLT 1 on VSPs) and just shutdown one leg. The value of MLT CURRENT should change from smlt to norm. Then try to reach the switch.
It would also be interesting to see "show vlan interface vids 1,2" and "show vlan interface info 1,2" on ERS. But I believe you've already doublechecked this.
I thought there might be a problem with SMLT-VIRTUAL-BMAC. But according to the output it is also set on both VSPs. So it is in state when you disable one leg of SMLT the ERS starts to respond?