Okay, look. He DID answer your question. In the NWN, there are really only 7 classes. Human, Elf, Half-Elf, Half-Orc, Halfling, Dwarf, and Gnome. Deep Gnome is a subrace of Gnome added in NS4. Considering its a subrace, your stats will be modified. The basic Gnome receives a +2 to constitution while the Deep Gnome does not. So, in NS4, that +2 you receive as a basic Gnome will be taken away when you change your race to the subrace of Deep Gnome. The only reason you didn't recieve the -2 to your constitution at first is because sometimes the Subrace Rods (these are the things that add on your subrace modifications) are a bit slow sometimes.
Did I explain it well enough?