The problem might be the width="100%" part of the tag, which, if the aspect ratio is being preserved, might stretch the image vertically too, and some renderers might do that upwards.
I recommend putting in the exact width and height, e.g.:
Code:
<object data="images/graafi.svg" type="image/svg+xml" style="width: 100pt; height: 100pt;"> <img src="images/graafi.png" alt="graafi.png" /> </object>
Change "100pt" to whatever the height and width are.
You could also put in "maximum-width: 100%;" if you're worried about it overstretching the screen.
I don't know if that will help.
My own personal experience has been that SVG support is still pretty inconsistent across various renderers--and not just in ePubs, but in web browsers and plug-ins, as well. (Plus, I'm still learning.)