Comment 20 for bug 782953

Good news (I hope).

Disregard the patches.
I looked at the code a bit more and added a "real" fix. (a pretty simple one, actually)
It was all because of that "modified_sourceslist" not being set to True.
I've commited the fix to the linked branch and proposed a merge.
With the fix, editing the sources in software-properties-gtk and then exiting will correctly display the update cache dialog.
This is a fix for Bug #1075537.

I tested this with the Software Center and, curiously, this also seems to fix this bug.
When editing the software sources from the Software Center, the Software Center "grabs" and hides the dialog and the update progress is shown in the Software Center.
After the cache update is complete, it executes update-apt-xapian-index correctly (though it takes a long time to finish) and, when done, it refreshes the Sofware Center.