all images of past post messed up after changing theme

Alignleft looks like it’s behaving itself exactly as it should: aligning the image left and the text to the right of it. If you want your left aligned images to behave the same way as you ‘align none’ image, simply go to your style.css and remove ‘float:left’ from your .alignleft code:

.alignleft {
float: left;
margin:0 1em 1em 0;
}

You can also change the margins to suit.