I had exactly this problem with my plants a couple of weeks ago. The "lipped" leaves that were affected were all in the top 1/3rd of the plant and the worst affected leaves showed the rusting/brown areas you also mention.

I overhauled my DIY ventilation system and it pretty much stopped the problem in its tracks. Some of the leaves that were not too badly affected went back to normal. But the more heavily affected ones kept the lip around the edge.

There are some pics of the problem in my grow log.