BUG: Research not updating.
When you have the "research tree" (RT) opened, and buy so you can't afford more research, if you then wait with the RT opened until you get enough money, then the RT doesn't update the graphics from red icons to blue icons.
To minimize checks against the money all the time, you can behind the scenes sort the research from low to high amount of money, then you only need to check against the next more expensive research (and maybe next less expensive too, just in case the user buys something elsewhere), instead of having to check every research every time the money changes.