Some clarifications on my patch above: It fixed two problems with resuming which I observed on my system (RedHat Linux 7.2); I make no guarantees as to how it'll work on your system. The patch will not do anything to let you resume old incomplete files which were on your system before the patched version was installed; it'll only help for new files. Finally, it should be noted that this patch will completely disable the "remove incomplete files after x days" feature; incomplete files will stay until you delete them manually.

More specifically, the patch does two things: Firstly, it removes the "isOld()" check when purging the incomplete file directory, because that check returned true every time for files which were in the process of being downloaded when the check occured. Secondly, it adds a function which loops through and actively stops all active downloads on shutdown. This because data on the downloads wasn't being updated on shutdown, but I noticed that data was updated when I stopped a download manually.

I'm sure there are much better ways of fixing both bugs, but I'll leave that to the real developers.