I've created a report in Report Builder 3.0 with parameters, and when I add it to the dashboard designer, I can see all the parameters from the report, but I cannot change it from <Default Value>. When I run the report from PerformancePoint, I can still select a value for the parameter, so it's not that the parameter is broken.
The parameter in question is a single-value param, with the available and default values set to "get values from a query", and was auto-generated by Report Builder.
Sometimes the auto-generated datasets erroneously require parameters. View the hidden dataset and go to its properties. Delete any parameters in the in the parameters section and adjust the query so it doesn't use the parameter. Once the parameters are gone, dashboard designer should be able to display the list.