No network connected, Maintain tool window closed after click "OK" button of the "Download Error" notification window.

Steps:
1. Start Qt Sdk maintain tool.
2. Click cancel when checking repository.
3. One Notification window shows there is "Download error".
4. Click "OK" button immediately, the maintain tool closes.
5. If you wait for 1~2 minutes, then click "OK" button, the maintain tool won't close and shows the package manager tab.
Issue:
The behavior is not the same when doing the same operation.