Likely, this is not a bug.
In yEd, text alignment is relative to the label box not the node size. The label box is the rectangle shown when a label is selected. By default, the label box has the size of the label text and, therefore, text alignment has no visible effect. You can adjust the size of the label box to the node width / height / size in the properties view (section Label, option Size).
You may want to have a look at the tools 'Fit node to label' and 'Fit label to node'.