Paphiopedilum with pleated leaves?

[Blueszz]

A while ago I purchased a Paphiopedilum hybrid (NOID, American). It has green leaves.
I think that one of the newer growths has pleated leaves. Not as the pleated leaves in the Oncidium alliance, but the pleating shows up in the length of the leave. This is the only leave that currently is growing.
Any ideas what caused this? Inconsistent watering?

I can't find any pests on the plant. After it finished blooming I repotted it. Roots looked very well. The new medium is much looser than the old medium and might hold water not as good as the old medium.
The plant is in the same medium as my Paphiopedilum Maudiae, which grows nicely after I repotted it.
Both are in my North faced window. As light concerns, the leaves from the Maudiae lost their color from too much light. Now this one gets filtered light from plastic sheeting that I attached to the window. The American hybrid with the pleated (?) leaves still gets full light thru this window and the color of the leaves is the same color as green as when I purchased the plant.

Temperature in this window: 64 - 71 F
Humidity in this window sill: 45-53 %

Currently my digital camera has the hiccups, so sorry, not pictures to share right now.

What do you think? Humidity? Watering? Something else?

Nicole