What type of soil are you using? If you're using a mix that has a lot of Peat in it like Miracle Grow...maybe its staying too wet and suffocating the roots? Also have you fertilized it lately...it might also be fertilizer burn or a combination of the two? I'm not an expert and just throwing out some possible reasons.

You might try posting this on the Container or Houseplants forum...you might get a little more answers. Good luck!

oooh! Mine looked like that when I overwatered. Sorry I'm no help, best of luck with it! You're new growth looks healthy.