Yea, they probably got cheap on security or personnel. This took a lot of skill to pull off, probably someone feeling undervalued.
If there's a mistake which pisses off one employee a company can probably get away with it (and misunderstandings are bound to happen) but when it chronically mistreats employees it's easy for pissed off employees to find each other.
My bet though, is that this is IBM or Intel syndrome, no one ever got fired for buying from (big name security) so they bought from them for a few years, (big name security) didn't really care about some specific element of (bank) infrastructure and so it slipped through the cracks.
Probably mixed with social-itis, friendly comforting guy who reassures gets position while scary crazy guy who constantly talks about potential problems is overlooked. Banks are pretty much the definition of conservative, chances are erring in this direction led to this problem.
Another option is some poorly implemented additional layer of separation designed to frustrate potential competitors ("We need to run your systems through this alternative implementation, so we can monitor your - entirely different yet, identical needs - yea it'll take a little longer and you'll have to pay us higher fees... are you sure you wouldn't rather open a "BIG BANK" franchise? Together we could really optimize home loan and transfer profits *Wink*!")