I've seen this in both the Axis and the Russian campaigns, where there will be mud or snow covering an area and an enemy unit without an engineer will spend their action entrenching themselves. I understand, for the sake of the scenario, that you want certain key points entrenched even if the weather is not dry and you don't necessarily want to hand out engineers to those troops (or can't if they're Russian). In those cases, I'd prefer to see the enemy start in their desired location, already entrenched because then I can at least pretend they aren't breaking the game's own rules.
Ultimately this is a small matter but it confused me early on (why are those AI troops entrenching when I can't and we're all caught in the same weather?) and somewhat undermined the games consistency.