I have seen this occasionally with some of my bananas. And I think only with the TC plants. I do not know what causes this, perhaps some type of mutation in the specific plant. I have never seen a normal leafed plant just start to do this, and it seems stable. I even had one that grew sideways along the ground like a rhizome instead of a corm! I had another, Dwarf Hua Moa, which typically grew only to about 2'-3' tall with gray leaves about 12" long and grew like a Fan also. It was so very unusual, a real "Liliputian" banana, it looked like a true Bonsai banana tree perfect in scale, not like Truly Tiny or other small bananas. The roots would continually develop and grow out of the P-stem upwards on the stalk until I had to cut them off at ground level and replant them! I have photos of both of these oddities in my members Photo Gallery. Look for the photos entitled "Mutant Musa" and "Musa Hua Moa Dwarf Fan" to view them, they are worth looking at! There is also another photo of a Dwarf Cavendish 'Fan' there.
Varig8
Banana Gallery - Mutant Musa
Banana Gallery - Musa Hua Moa Dwarf Fan
Banana Gallery - Dwarf Cavendish Fan-top view
Banana Gallery - Dwarf Cavendish Fan
Banana Gallery - Member Profile