RSTP on EX3400 et interface

Hi together,

I have a little problem with two EX3400. These switches should use rstp. Both switches have two uplinks  to two different switches via the et interfaces on the back of the switches. The rstp config looks like thes:

set protocols rstp bridge-priority 32k
set protocols rstp interface et-0/1/0 mode point-to-point
set protocols rstp interface et-0/1/1 mode point-to-point
set protocols rstp interface ig-l2-edge edge

If I connect the second uplink I create a loop in the network.

With other switches (EX4300) it works fine.

Is there something special in the config?

Thank you for your help.