XnView Software

I have a large number of categories which I view from the categories pane and which requires uses of the vertical scroll bar to move through them. I am forever finding that I have inadvertently picked up a category instead of the scroll bar and moved it to somewhere else in the category hierarchy. Strangely, moving it back using drag and drop is never that easy and I always resort to the right click/move to option. My suggestion would be that the drag and drop is not a so much used operation and could easily be left to right clicking,

described issue (guess you are using trackpad) shall be solved by introducing "Lock categories" setting instead of removing drag&drop functionality

Yes, that would do it and would have the advantage of being able to work with a project specific set of categories without adding loads of unwanted ones if you open an image folder containing images with a different set of categories. It is currently the case though that wysiwyg - if you select an image the values you see assigned accurately reflect what is in the XMP data rather than a subset of the values filtered by the current category list.