No luck so far.
1. I unplugged 10 GE Ports -> no change
2. I deleted the 10GE VC-Ports -> no change
3. I rebooted both switches -> no change
here the situation after the three steps:
root@qfx5110> show virtual-chassis vc-port
localre:
--------------------------------------------------------------------------
Interface Type Trunk Status Speed Neighbor
or ID (mbps) ID Interface
PIC / Port
0/48 Configured -1 Down 40000
{master:1}
root@qfx5110>