another thing is that u can get roots that sprout all over the place... vandas love having roots exposed to the air... so maybe its just trying to sprout a root outside the potting material???
as u can see from this image (or not so clearly) is that the whole bottom foot or so of this plant has roots coming out all over the place... also the plant to the right has the same roots...
again im just speculating... could be totally off. hope this is of some use though!