Empty space under image in RTF

[Ninca]

Hello,

I want to structure my generated rtf document like this:
 - overview diagram containing uml elements
    - element in diagram, e.g. use case: heading + text description + image
    - element in diagram, e.g. use case: heading + text description + image
    - ...

This images are in an image format (.png, .jpg, .gif).

I did realize this RTF structure by creating a (interaction overview) diagram under the element which only contains one image.

When I create a RTF-Document the image gets automatically drawn right under the text. Below the image I  configured a caption in the rtf template.

And here my problem:
Sometimes in the generated diagram-image there is a white space (about approximately 2 cm) below the original image contained. It seems to me that if I change any settings of that diagram (Properties-Tab Diagram) then no white space is drawn below the original image - but only until I close the program and restart it. Then its there again though I did Save all. That's really nerving.

Is there anything I might do against it?