Whether intentionally designed this way or not, I have no idea–but this is working correctly per the existing configuration. The Soviet infantry and armor units both have a Mask trait and start in decks, so whoever pulls one of those off their starting decks masks it with their personal module password and becomes the owner of the piece. Non-owners can’t flip (unmask) it from that point, only the player who drew them off the deck can.
To override this, all modules have a global option you can set in the Editor: Allow non-owners to unmask pieces.
In this module it’s currently set to Never, you’d have to change that if players are meant to be able to reveal each other’s pieces.
You won’t be able to edit if you currently have it open for play. If that isn’t the case, report back with exactly where the module file is located in your filesystem–mostly want to verify that you are not storing the module in VASSAL’s installation folder (if using Windows).
Interesting. I don’t know enough to predict what’d happen if you make this kind of module edit during an in-progress game. It’s possible that only newly-drawn pieces can be flipped by non-owners. The worst case is that you’d only get the altered behavior after starting a new game. I’d have to do some experimenting to figure it out unless @Brent_Easton knows offhand how this would play out.