Antonio,
Is 8806 port 6:2 connected to Stack port 2:49 (i'm assuming so)? Are there any other active ports in mvrptest?
In order for MVRP to function, there should be multiple devices advertising the VLAN in the network. It is intended to dynamically extend/provision a VLAN, advertised by two edge devices, across the core of a network. Try adding another active port on the 8806 to mvrptest (not 6:2). I suspect you will see 6:2 added dynamically to the VLAN at that point.
If not, please post the following outputs (from both switches) and we can investigate further:
show vlan
show vlan mvrptest
show mvrp tag 200