I've got a path with a fence on either side of it. The fence has a clip on either side of the fence, but it doesn't obstruct the path at all in Radiant. There isn't some hidden patch or brush in the path, and when I delete one of the outer clip patches, I'm no longer blocked in-game.

So it's like this: 

clip -fence- clip   --path--   clip -fence- clip

I've looked it over several times, recreated the patches multiple times, ensuring that there isn't a vertex hanging out inside my path, but regardless of the fact that none of the clips pass through my path, it's blocked when all patches are present. What's going on? (I can post screenshots or a couple of GIFs showing what's happening if needed)