on the procurve sw:
lacp group 1 is its own interface made up of 2 ports, and that interface is now known as trk1...
lacp group 2 is its own interface made up of 2 ports, and that interface is now known as trk2...
when you create lacp groups, those new interface definitions will automatically be untagged in vlan1...the individual ports will actually be removed from all vlans they were defined in (untag or tag) at that point...the individual ports lose their individual definition as they are now part of a trk"x" interface definition...
when you connect these to interfaces (trk1 & trk2) between the 2 switches, and they are in the same vlan(s), you get a loop...its just as if you connected two single ports (not in a truck/lacp config) between the 2 switches...
if what you are wanting to accomplish is at least a 2 port link that will do load balancing and provide a larger path between the 2 switches, then you can simply configure a single 2-port lacp group on each switch, then you connect the switches together on those ports...
again, the lacp protocol/definition provides for load balancing without any other separate configuration required...it just does it...its based on dest mac addr from each switch's viewpoint...
hth...jeff