I'll tell my story.

I had a content type with a CCK field as Private Number (PN) and some others text fields. PN store data encrypted.

I did a mass change to a text field with VBO, and after that i lost all the PN field data.

Later i realized that VBO changed the PN field data with the encrypted one, so now in database has the encrypted encrypted data (double encrypted). For some reason, VBO got the masked version of the field and saved it (VBO could only gets the encrypted value). Maybe it's something about permissions, but i can't see where to give permissions to VBO over a field or else.

I thought it could be a bug somehow but, after a long thought, it's logical that VBO couldn't get the right data, that's why it's encrypted in the first place.

So, i strongly suggest that should make a note about it on PN main page alerting who uses PN and need to bulk modify a CCK field with VBO.