Absolutely...

The BHD flights won't be going to T5 for as long as BA codeshares with EI (for precisely the same reasons that BA's services to SYD & SIN [same as QF's services on these routes] and to HEL [same as AY's services on this route] depart from T3).

BA could not sell tickets to a single destination on flights that may depart from different terminals - relying on every passenger to correctly decipher the flight number to get to the right terminal just would not work.