Something is wrong, obviously! The Reth works like active back-up. The secondary Node keeps the interface Up, but never sends and drops all receive. So you can not run an AE from the EX to the SRX Reth (Think only one Reth) as EX AE will always think both links are active, while in fact one link is a drop all.
The EX will learn MAC and IP/ARPs on the active link only, so it therefore knows to use only the active link in the Reth. This is somewhat similar to how RTG works in EX. Maybe send your complete EX config without the AE's configured. A Reth of 2 phyical links, 1 active on Primay Node and 1 in standby on Secondary Node would have no LACP as NOT an AE to start with.
What does show chassis cluster status look like on the SRX Cluster? SRX Cluster config is right, yes?
You should really troubleshoot this with Juniper TAC, I'd say call in under SRX not EX.