If the sample data is incorrect, it keeps using the previous data

[Koning53]

If you enter and edit sample data in the sample data editor and make an error in de JSON:

• this is not clear there is an error in the sample data
• the preview is still based on the 'old' data of the sample data editor

It took me quite a while before I figured out this was the cause of my template not to work. I would expect the preview to fail and show a message about an error in the sample data.