I have a very strange thing happening with image uploads using the Media Uploader add-on. All images get uploaded because I can see them in the media library but only a few actually show up in the comments.
I thought maybe it is a problem with different types of images so I tested it with jpeg images only. It seems that smaller images get displayed and larger ones just uploaded but never appear in the post.
They also don't appear appear as the small thumbnail under the form after the image is uploaded just before you post the comment.
Maybe there are some settings I have overlooked? I send you a screenshot of my settings.
Also when I paste an image directly into the comment like that ...
it looks like that after posting the comment:
I tried it with jpeg and png images - same result
All the images except those directly pasted into the comment form are actually uploaded and appear within the media library: