Force carbed a new s-type keg. Leaking this morning.

[BrewVerymore]

I have a brand new S-type keg that I filled up to near 20L (1/6th). Everything went fine. I hooked up the coupler to my keg and pressurized to 15psi. I woke up this morning (8 hours later) and found that beer seemed to have leaked out and onto the floor of my temp controlled freezer. It was a small amount, about half a cup. I pulled the coupler to the up position and twisted it off. Beer rested in the little dip where the spear/valve is but there was no visible leaking of any sort.

Any idea what could have happened? It's a brand new keg and it was twisted on properly. The leak seamed to be coming from where the coupler meets the spear, not from the beer out. The coupler is used but I also do not know what to look for. Any help would be appreciated.

Update- I've added some photos below. You can see that the beer is resting in there. There are no gas bubbles or anything coming from that entire rim area. I'm not sure how it's coming out.

 

[BrewVerymore]

I feel like an idiot. If you'll notice there I have a gasket between the coin and the wingnut where I should've had it on the inner side. Well it's fixed now -_-