Replacing the File in Image Content Types

Hallo,

I installed TinyMCE, Image Assist and the TinyMCE-Image-Assist-Plugin. It works all right.
But when I change an image-node, the changes are not applied on the pages.

For example: I have a Portrait in an image node. This Portrait is inserted on five pages (with image assist, not html but with[...]). I change the file in the image node. After this, the image is not shown in the expectad way, it is gone- I have to do "update" on each inserted place to have the new version visible....

Could anyone tell me
a) if it should be normal, that the image is shown in the newest version, when I change the node
b) some ideas, what I could do to achieve a)

Regards

Adriana