Generally It Is Thought To be Related To Water Or Humidity by: Melissa
Hi Anne, Thanks for your question.
It is a relatively common occurance. I know I have had several do it over the years.
I have always "heard" that it had to do with not enough humidity. But the fact that you mist the plant often would tend to indicate that it is coming from something else.
I went and check out some of the orchid forums and as I thought, many folks think it is related to humidity.
But there were several who thought the thicker leafed Phals. had a tendency to do it more than the thinnner leafed ones.
Several people thought that it might have to do with the media drying out too much and then being hydrated and the change in water status in the plant causing the tissues to swell and burst. It usually happens down the center of the leaf.
It was generally thought that it did not really cause a problem with the plant other than the fact that it did not look so good.
Sorry I can not be more informative but it seems that there is probably not one cause and that the cause does have something to do with water status.