I mean when I'm back to the app I see all contents of this folder in right pane as preview but I have to enter a password to browse this folder. It's strange behaviour.

So this should be a feature request - to make an option: full lock or do not lock protected folders when program is minimized.

When you close program to tray, you simply minimize it, which assumes it's still open and therefor you don't have to enter your password again to access your data once you're back to the app.

I'm using 3.14 beta

Click on protected folder and enter a password, then just don't select anything else and close program to tray. Open it again and you wil see all contents of that folder in right pane as preview. So it's unsecure now