Nope, had enough gold. Had about 21 stored away and lost 12 I think.
I can't say for sure, but I think that DaveMcW is right:
If you only had 21 left, and NOW you're at 9 (i.e. -12 for the last turn), then the game probably changed your tech rate to get you to this point; if it HADN'T switched your science%, you probably would have been -22 or worse for the turn, thus, it changed your science% so that you didn't end up with -ve gold...
Is it possible that some event between turns lowered your commerce?
- maybe international affairs affected your trade routes
- or the Governor switched some city tiles around, or he did something with specialists (took off a scientist for example)
- perhaps a city grew and hit the unhappy cap and stopped working a high-commerce tile as a result
or any other number of tiny events...
in BtS my cities changed tiles even when they're set to manual. drive me up a tree!! happens even during a turn, before i press enter, when workers are done making an improvement. and i swear i don't use the city governor grrrrrrrrr. i don't trust that guy. that's supposedly gone since the patch, and i think it is better now. have you patched?
even since the patch, i see weirdness when i change the slider. it'll say +120 gpt for the new rate at first and then it'll quick change to +123, stuff like that. i don't think that's a lag in math, it may be tweaking a tile or a specialist just based on moving the slider, but i haven't ever checked every city to be sure. but something freaky is going on there.
I've seen my gpt vary as much as 20 or so each turn, and not when I'm whipping people! Though this is very late into the game, it does happen.