Posting: images from “upload/insert” not formatted properly

When making a new post you can click on the buttons next to the word “upload/insert” to place an image in the text for example.

I place an image, chose it to aligned to right as an example.

In the editor (wysiwyg) it aligns to right.

But once posted and at the actual blog the picture is not formatted at all. It just resides there as a normal img without align formatting (or any other formats/stylings)

I checked up the CSS code for that image in that post and it is “alignright size-medium wp-image-41”

I then went to the style.css and looked for this class entry, and found nothing.

How can I do to get this to work?

I use the latest WordPress installation together with a theme I downloaded and works nicely otherwise. I am fiddling with that theme now, but this image issue has always been there.