Lighter spots on top of leaves, dark bumps on bottoms of leaves

[reptilegrrl]

Most of my oncidiums have something like this on one leaf or another, and so I figured it was probably normal, but I haven't seen it mentioned anywhere or in photos.

I took a photo of my big oncostele. This is the only plant where the issue seems more intense at the center of the leaf.

The top of the leaf appears to have some slight spotting- lighter spots scattered around the leaf. The bottom of the leaf has many dark spots as are typical of onc-type orchids, but in most cases they correspond somehow with the light spots on top. And in the center of the leaf, beneath the largest light spot, there is a hard, dark-ish, irregular bump. All of my onc-types have something like this, but none as big as this one, and none that seem to affect the top of the leaf. Is this a disease?

I do not share water and this orchid came from a source different from my others. ALso, there's no evidence of pests on this or any of my orchids.