Reported by norrumar on 2013-07-09 15:51
NVDA allows to open addons manager when it's already opened. This produces an error when trying to close this dialog.
Step to reproduce:

1. Open the addons manager.
2. Open it again.
3. Try to close this dialog.
   Actual result: It's not possible to close it due to a dead object error.
   Expected result: Dialog shouldn't be reopened.