Generally BA staff have seen this issue regarding charges with Iberia coming. BA need to be a lot more prominent stating that flights operated by Iberia will find passengers charged if they are on a eurotraveller ticket.
Swiss and Aer Lingus do the same and BA codeshare with them as well.
Mind you on the BA flights the passengers demeanor doesn't seem to improve when the Iberia or Aer Lingus ticketed passengers suddenly find out it's all for free, their still as grumpy.
I don't see where this can be resolved because at the moment BA is still commited to not charging, see where it goes.