it seems to me that there is a problem rendering a shapefile during the save of it.
I tried two times and got the same behavior so think this is general.
If you create a new shapefile, in my case it is a point shapefile, and progressively populate it and visualize it choosing some preferences in the style (like visualize the labels) when you save the shapefile, the style format will not be reloaded.
If I take a look in the style editor I can see that my preferences are still selected but not rendered.
So for rendering the labels I tried to select and deselect the preferences and apply the old and the new ones, without luck...
Just restarting udig all will be rendered perfectly...