[BUGFIX] phpcr value format change exception try to delete property and rewrite it

__Tasks:__

- [ ] test coverage
- [ ] gather feedback for my changes


__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | none
| Fixed tickets | #544
| BC Breaks     | no
| Doc           | none
@wachterjohannes does saving the session in the content type made any problem with the refractored preview?