One solution! I had the same problem. I noticed that Tobias' hat had pixels on the hat on all four sides, but kumasasa's did not. I found that by removing the pixels on the bottom of my previously full hat fixed the problem. The issue is, apparently, with having pixels on all six sides of the hat. At least one must be blank. Only tested on 1.8.1 creative singleplayer.
Piman777
One solution! I had the same problem. I noticed that Tobias' hat had pixels on the hat on all four sides, but kumasasa's did not. I found that by removing the pixels on the bottom of my previously full hat fixed the problem. The issue is, apparently, with having pixels on all six sides of the hat. At least one must be blank. Only tested on 1.8.1 creative singleplayer.