Why does the STORE button on Amazon Kindle go to the website instead of the in app store?

I have the **Android Amazon Kindle** app installed on both my **Galaxy S phone** and my **Archos 10" tablet**. I keep the software updated so I'm sure the latest version is installed. I am logged in with my account on both devices. When I press the STORE button I go to the inprog Kindle store. But when I press the STORE button on the Archos it starts the web browser in stead. Now, I have bought ebooks before from both devices and I am sure that previously, the Archos also displayed the inprog store. It's much easier to use the inprog store display than the full Amazon web site version. **Does anyone now what could have changed this behavior ?** I looked for some setting but found none.