How exactly did you create this specific SO?
Could it be you opened a RAW file as a Smart Object?
Sound like what was mentioned above: you dragged a RAW file or one that was at somepoint edited in ACR into your document. If you open a jpg or other file type in ACR, it will continue to open in ACR, so this might be your problem if it's not a RAW file. You can check to see if it was edited in ACR in Bridge. There will be some icons below the thumbnail showing that it's been cropped and adjusted in ACR. If the files you're trying to drag in aren't RAW or have been edited in ACR, this sounds like a bug.
Okay, not 100% sure. These are jpgs, but I did drag and drop them. So, a jpg Smart object has different properties depending on how it is brought into the doc. If I drag and drop, I won't be able to edit the layer as a .psb. But if I open it first, convert to SO, then copy the layer into the doc, I then have my SO editability back.
Yes, I believe so.