Version: 1.4.2 (using KDE KDE 3.4.2) When a user is editing the attributes, he edits them through the "attribute properties" dialog, which is opened from the "properties" dialog. Because the "attribute properties" is created as a new window outside of Umbrello, if we click in a place outside of that attribute, the "attribute properties" dialog is pushed into the background and disappears from sight. Consequentially, the "attribute properties" dialog is hidden and Umbrello is shown but it is inoperational because the focus is still on the "attribute properties" dialog.
It has been fixed in KDE 4 version: the dialog window is now modal.