I have a form with a CollectionType with a subform. I'm trying to upgrade my project from Symfony 2.5 to Symfony 3 and face a regression.

This subform has a twig template with, among others, horizontal_label_class and horizontal_input_wrapper_class parameters for some widget. If there is already some data in the collection, the generated form is fine and respect those parameters. However, the prototype generated is incorrect and does not respect those and the UI is broken when dynamically adding new entries in the web page.

I tracked down the origin of the regression to this PR, introduced in Symfony 2.8.5.
#18317

If I roll back the three lines change in CollectionType from this PR (https://github.com/symfony/symfony/pull/18317/files#diff-148c9ca81f4d248cb20ab6ae2a3219f4L58), everything is fine again.

Other related issue:
phiamo/MopaBootstrapBundle#1167