Wierd and frustrating problem in "Behind Enemy lines"

[Anhvu]

I'm playing this russian campaign mission on normal diffculty settings.

I don't understand why, but I keep getting a warning saying that I leave too much evidence behind. I don't see how that is considering that I haven't been spotted at all. There absolutely no warning of any sort that I been alerting the guards. In fact, I get this warning message even before I penetrated the german defense line. As a result, the stealth lvl ends with objectives failed and I'm forced to fight against the Seelow Heights defenses.

It is really irritating, that the mission might have a bug. I also have noticed that the AI tends to randomly wander into the no-man's land between the trenches, do you think the AI is setting off the alarm? how can I fix this?