I get the same with my Psittacorum heliconias. They're in the ground and only in one area that happens. They don't get much fertiliser but they all get the same treatment. The only thing I can think of is that this spot is much wetter/ more water retentive than the other areas. That's only a guess, but it's been happening for years and none of them seem the worse off for it. I gave up worrying/thinking about it.

Trop, do your light green leaves remain that color? If so, then after original leaves departed, entire plants are light green?

On mine, the leaves stay a very light green. The only dark green leaves are the ones from the original plant.