How many uplink do you have between MX and EX?
Case 1 -
if it is only 1 uplink then, you need to allow all the vlans on MX side as well.
As per your description you seem to have allowed only vlan 10.
"(on MX port I have: type trunk ; native vlan 10; allowed vlans 10) "
Case 2 -
if it is two uplinks between MX and EX,
then you need to allow specific vlans (except vlan 10) on working uplink 1 where your routing is taking place. (10.1.x.x.)...
Hence, on EX 4300 you need to configure "vlan members [ 1 2 3 ...etc]" and need to remove statement "vlan members all"
On second uplink allow only DMZ vlan (vlan 10) on both MX and EX. port mode may be access on both sides.
HTH..