Well it looks like you have 1,008 infrastructure now, so unless you're selling it or being attacked, I'd say it's unusual and probably a bug. Unless in the remote possibility your nation has summoned spirits and devils, but in that case, I think you have a lot more to worry about.
You should note, however, that 1,008 infra will cost you a lot more in bills compared to 999.99, without much extra in collections, so I would actually recommend selling off a few until you can buy a whole bunch at once to surpass the extra costs, which is referred to as an "infra jump".