Latest update.
I replaced both switches with one Juniper EX2200-48T split to 2 VLANS with access ports, one for the public part and one for the LAN.
All is working very well, and as expected.
So basically if I surround the OpenWRT with standard compliant switches, they manage work around the noncompliance of OperWRT itself :).
I ordered one Cisco WS-C2960G-8TC-L, which is fanless and I will try to replace the Juniper with it and hopefully the cisco one will be ok too.