EPiServer.Forms breaks collection editor / PropertyList

Description

The collection editor / PropertyList (.epi-collection-editor) becomes scrollable once you add enough items. However, after installing Forms addon, this functionality breaks.

Steps to reproduce:
1. Start the Alloy website.
2. Add IList<T> property to any page type (where T is a complex type).
3. Set up a property definition type plugin accordingly (http[://world.episerver.com/blogs/Per-Magne-Skuseth/Dates/2015/11/trying-out-propertylistt/]).
4. Edit a page with the new property, and add enough items to the property to make it scrollable (10+ items).
5. Install the EPiServer.Forms addon.
6. Rebuild and browse to edit view of the same page.

Expected:
The collection editor/PropertyList becomes scrollable once you add enough items.

Actual:
The list editor is about half of its previous size, and cannot be scrolled