Did you ever consider a bacterial or fungal infection? whenever i do stuff like this, i use a strong copper oxychloride mixture at half strength, once a week for about 6 weeks. i spray this over the substrate and plant/cane. This greatly reduces the chances of an infection as it sounds like you have.
I then use a half strength orchid growth booster, one formulated for orchids that is, when the little roots begin to appear. I do this again, once a week AFTER the copper regime is finished, for about 6 weeks again, then pot out.
Just my two cents worth, and i hope it helps!