When updating to v1.10.0-beta1 from v1.9.1 the overflow settings in existing blocks are lost and cannot be set again.

Steps to reproduce:
1. Install v1.9.1
2. Setup two Schedule blocks (names: S1, S2), with overflow from S1 to S2.
(Navigate to Page -> Edit -> add two Schedule Blocks -> set overflow from S1 to S2 -> Publish LP)
3. Update to 1.10.0-beta1
> git pull origin refs/tags/v1.10.0-beta1
> git checkout --theirs composer.lock && git add composer.lock
> git checkout --theirs composer.json && git add composer.json
> composer update
> php app/console cache:clear -e=prod
> php app/console assets:install --symlink -e=prod
>  php app/console assetic:dump -e=prod
4. Navigate to previously modified Landing Page
5. Check the settings of Schedule Blocks

Expected result:
Overflow is set as previously (from S1 to S2)
Actual result:
Overflow is not set

Trying to save the overflow (setting it, clicking Submit and then Publishing the LP) does not save the overflow settings: error is thrown (console_error attachment), but this might be unrelated.