Adjusting the settings for "Collapsed" has no effect on datalists whether false or true is selected. This is occurs on both forms for SDK and the design mode with any data list in CRM.
The Collapsed nature of the datalists are meant to be sticky values that change based on user input. The Collapsed property does not apply to datalists. If you want the datalists to be collapsed, collapse them and they will remain sticky. If you want them expanded, expand them and they will remain expanded.
Steps to Duplicate
1.This works on any datalist in CRM but Click Events tab.
2. Select an event with a datalist
3. Select the registrations tab.
4.Toggle to design mode.
5.Select Properties and adjust Collapsed field to "True" or "False" and click Save.
6.Notice that Collapsed setting doesn't change no matter what it's set to.