I've encountered a strange bug lately which lead to the possibility of endless spending. Gold spent for adding production was correctly deducted in city screen. Leaving screen and returning to map: voila the gold was resetted as beginning of turn. I tested it and it was possible without problems to spend gold on a 2nd new production. The game wasn't influenced however as it was already more or less decided. Production did never enter battle.
Now in a different map i have the strange suspicion that this behaviour continues to exist. A warring neighbour of mine in that game (id 3768) started to show to have his 2nd quite expensive production here (both 1000+ gold required to build). The deal its still a game not in its infants but at least in the beginning of a mid-game phase. Any GM could check the game log for irregularities? I can be quite off with this (lucky ruin raids - very well possible) its just a guess into the blue but having encountered such a grave problem i'm worried about possible cheating deeds.