Game version: 0.95.178

When playing with the unlimited economic buildings option enabled, multiple 
banks on one planet have no effect. If you have an upgraded bank and build 
another one, the second even cancels the effect of the upgrade on the first 
bank.

While this isn't a problem for the player, once you realise this, the AI builds 
multiple banks on their planets. Either the effect should stack (this could 
ruin the balance though, I fear) or the number of banks should be limited to 
one, even if the number of traders spaceports and trade centers is not, so that 
the AI doesn't spend loads of credits on useless buildings.