Analog film photography and cameras

That's definately an agitation issue, or if stand developed then it must have been caused by the flow of developer into the tank, but it's usually a symptom of insufficient agitation. Nice photos though.

I got this on film recently, really badly but only on one or 2 frames and I was agitating well.
Any ideas?

Edit: Here's the worst image http://www.flickr.com/photos/andephotographic/5580462763/ and yes I know it's also got a massive light leak on it.
The previous image in my photostream is the only other frame where this was visible.
Is it possible the film wasn't quite as it should have been in the spiral and these frames didn't get proper flow of dev around them?