Version: (using KDE 4.0.3) Installed from: Fedora RPMs This appeared to me in Thunderbird, together with KDE4 and gtk-qt-engine (with options to use KDE themes/looks). The progressbar actually starts too far left. As progress moves on, the problem resolves. So I guess it might have to do with a progressbar trying to display "too few" percent and occuying some minimal space, which then shifts the image to the left.
Created attachment 24780 [details] Screenshot of progress-bar being too far left
Not a plasma bug.
This is not a KDE bug. Please report it to the gtk-qt-engine authors.