Data disappears from encrypted box once it is opened without cypher

[ig-garcia]

I did a test project with only Dart (no platforms) and this happened:

I opened an encrypted box and stored some values, then next time I opened the box without encryption and when I check the box.values they are empty.

Is this expected in any way? How can I check if my box is encrypted? I was expecting that I could check whether the db is encrypted by getting some garbage data. Even if I open the box with encryption again, it is always empty after first time.