[Backport 7.9] - Boolean fields in existing documents are unchecked while closing all tabs

Reproduction steps:

1. create project based on archetype
2. add the simple content feature from essentials (rebuild not necessary)
3. in the CMS document type editor, add a Boolean field to the type
4. save the type (type actions / commit)
5. create a new document from the new type, check the boolean field, click Save & close. Leave the tab there (don't click the red X-icon on it).
6. Right click on the document tabs, choose "Close All".

Expect: can close all documents without changing values
Actual: A warning "There is a modified document" popup, the boolean field is unchecked!.

This changes the content of documents in a most curious and unexpected way and should be fixed as soon as we can.