Ground plane: pad does not connect to it

Hi, 

Another newbie question. I run OrCAD PCB Designer Standard V17.4. 

I've created a part in Capture : 

Nothing fancy here. And as you can see, I have pin 16 attached to GND. 

One in PCB Editor, I placed evertything then pour a ground plane (dynamic) and assigned it to GND net. 

As you can see, most of my parts got their ground connections made to the pour. For a reason I cannot understand, a few parts did not get connected to the ground pour. As you see, the parts on the right got connected automatically but not the part I created and some others (more on that:see below). 

The part I created as pin 16 as a power pin : 

I also created a specific padstack for this part with the following parameters : 

I also have a few other components that did not connect automatically to the ground plane. I haven't inspect all of them yet, but it looks like those are the parts I've created using Ultra-Librarian. I worked-around this by creating a static copper shape attached to GND around the pad. Still, I would like to undestand why is that behavior. 

Many thanks