Looks like we can't reproduce the issue or there's a problem in the test case provided.
TreeStore can't get data from url in web but can refresh it in designer.
It's a wired problem, when I set all down, I can refresh the TreePanel and get data by url:'areas.json' in Sencha Designer(288), but after I save(deploy) it to tomcat, I can get nothing in web ( Panel already rendered). It that a designer bug or my mistake?
Well, I fixed it.....After I set rootvisible to true.
Glad you were able to resolve your problem