Though you may be right, I suggest you take a closer look at what is happening, Klaus. I'm not at all surprised that it downloads comments because the publish process is hard wired to do so (the plug-in author would have to deliberately add code to intercept the request for comments). But it does sound odd that files weren't exported, as a minimum, and then uploaded from multiple collections. An export, usually to a temporary folder, should always happen as a result of pressing a Publish button, and LR then allows the plug-in author to define what happens to the exported files, in this case uploading them. A plug-in could conceivably block uploading if more than one collection is selected, but the plug-in author would have had to implement this deliberately with some unusual code, which would be surprising in two plug-ins.
Klaus?? I was reporting what happened when I tested this after you wrote about the option click publish behavior. Yes, it is no surprise that the comments are downloaded as they always get when doing a publish, but no upload happened neither of new images or modified images. I also tried with the Jf Collection Publisher that I use for synchronizing with my iPad and also this one does not upload images using the option click publish.
If there is a group of folders, selecting the group and click (not option click) publish will upload images in all folders within the group. E.g. http://www.hanskrusephotography.com/Landscapes
if I marked pictures in different subfolders to be republished then selecting the Landscapes group and publish uploaded all images in subfolders. In fact I had never tried this before and only thought about it because of this discussion.