I can copy/paste an image on the editor and get a small editor window to change the image attributes (which is not bad) but it does not show up if I save the edited page. In fact, all the image code (raw image) disappears after a save.
PS: But it works if I copy and paste the html code from an external page (images from external links are appearing properly).
Is that page in HTML mode? If it was made before you disabled the "wiki in wysiwyg" preference then it will still be wiki mode. Try it on a new page - or switch to wiki mode (the yellow pencil button) and back again and it should be in html (and you can see that in the page history).
Also i seem to remember the resize image in the editor thing only works in some browsers, so maybe try Firefox if you're not in that already?