Unable to add system_download_list container

[dantefromhell]

When creating and editing a template based custom page, I'm unable to add the build-in container type 'system_download_list'.

The editor gets stuck on the "Add system_download_list item" screen shown below, clicking Save makes the modal flick/ rerender but the container is not added to the page.

Steps to reproduce

• Create new page based on Template
• Add a 'system_download_list' container
• Give it a name
• Click Save

HumHub version 1.15.5 custom_pages: 1.10.3