Hi there,
It sometimes so happens (mostly when downloading resumable http links) that a link that is downloaded is only valid for a certain time. Or maybe the link becomes unavailable in one location, but is available in a mirror location. So if you stop the download and try and resume later, it will not resume without changing the location.
What is necessary is to enable a feature to change the download link of a particular file. (by right clicking file and selecting properties, then you should be able to edit the URL field)
This is comparable to IDM where you can right click, go to properties and then change the 'address' field.
Regards,