If you would see that we see daily how many bugs are coming from modification please believe me your first question would be the same :)
The scheduling system is a fine balance; we cannot simulate real world as we can't move idling planes from gates and we don't track the registration number of the planes to make sure the same airplane leaves that arrived early. We wrote a system that works most of the time so there are possibilities when we won't have enough gates, etc. When you read no free terminal for departures it can mean something totally different. We told/asked many times the log file is for us to help you when help needed, not to troubleshoot things on y our end.