Steps to repro (version 1327):

1) Open existing project or create new project
2) Create new Manual test - leave it empty
3) Add Manual test to a TestList
4) Click "Run List"
5) When the manual test runner appear immediately press 'x' to close it
6) This will generate a failed result in the Result Calendar
7) Go back to TestList view
8) Press run "Run List" for the same TestList
9) From the menu that comes up select "Edit existing result"

Result: Unhandled exception.