In the most recent update, I found that editing an item with multiple canvases (such as the Crystal Ball or Haunted TV) will only ever show the preview for the canvas in the list, rather than changing for which canvas you have selected. In the past, I seemed to remember the preview working for each canvas individually.
I also happened to stumble across another issue while testing this. I closed the item editor while hovering over the quick preview, and it ended up permanently affixed to my cursor while I moved around my condo.
