Hi cslacker,
Juniper reserves vlan-id 0 and 4095 for internal use. These vlans are not available for use by customers. Other vlan 1 to 4094 can be used by customers.
A physical interface can have 4094 sub-interfaces for 4094 (1-4094) vlans.
A subinterface always expects a vlan tag and due to which you are losing connectivity/ospf neighborship on your 10.0.0.0/24 network.
Please refer to the following links.