Aligning images inside post does not work properly

Hello,

I just put an image in a post and I want it to align left, have the text flow around it with a 5 px space.

The css class reads: alignleft size-medium wp-image-436
And the Style is: margin: 5px;

I used the default image editor of WP for this. But as you can see here:
http://www.aanbiedingenvakantiereizen.nl/aruba-…zonovergoten-eiland/
The text does not flow around the image as it should and as it shows in the wysiwyg editor, see screenshot.
How can I fix this?

[attachment=2179]screenshot.jpg[/attachment]