Hi Jonathan Perry,
You might experience this behavior if you have used the selector to set the page. There is a bug that will be fixed in Sitefinity 3.7 SP4.
The options are
1. Set the property manually - type the url without using the selector.
2. Expose DestinationPageUrl on the first level and use the selector
and add the code below to it
.Login1.DestinationPageUrl = value;
When you open the designer you should see the
property on the fist level.
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