Width of information section on Details page changes all the time because of numbers formatting.
When e.g. "Download payload speed" changes from "0 KB/s" to "99.6 KB/s" the section (together with the progress bar on top) becomes a bit wider. And when the speed changes to "98 KB/s" it shrinks back again.
Those constant shifts are quite annoying.
And I would suggest implementing a fixed layout.
By the way, why not to use the whole width of the window?
Even on demo screenshot on SourceForge there's plenty of space on the right.
And if you stretch progress bar and information section to the full panel width (but not less than some minimum size, of course) the display will become more "polished" and there will be no such "jumps".