I got a definitive answer today as to the cause of at least some of the problems discussed in this thread. I've had the same problem as shown in the previous photo from srash and described by Brent -- cigar leaves that won't unfurl properly, get burnt, and end up bent when unfurled. A photo of my dwarf cavendish with this problem is at the end of this post.
Dr. Scot Nelson, the writer, director, producer, etc. of the great fee DVD, "Growing Bananas" explained to me what is going on...
The ultimate cause of the problem is calcium deficiency. But many of us have noticed the link with fertilizing. What happens is that if availability of calcium is low but nitrogen is abundant, the plants grow faster than they can transport adequate calcium to the cell walls of the growing leaves.
The short term solution is to apply a foliar spray of a liquid calcium product. The longer term solution is to add calcium to the soil. Dr. Nelson recommended an application of agricultural lime to the soil every year or two.
Finally, mystery solved!