I'm afraid I cannot reproduce that? Must be hard to find out, but if you find a precise list of actions that makes you unable to select items that'd help a lot!
A recipe is:
create a statusbar;
add a progressbar to the status bar;
click on empty window (window properties are shown, ok);
click on progressbar (the element's properties are shown, ok);
release the left button, window properties are shown again, you cannot edit the progress bar element.
add a new element i.e. a new progressbar;
now you can select any of them and property panel works correctly until you click on the empty form again.