Determine if uninstall was called from upgrade

[xoopus]

When running the installation for a newer version of an application the previous version is uninstalled. I have a custom action in my uninstall that I only want to call if the user is uninstalling, not if the user is upgrading. I tried setting registry flags in the onbeforeinstall custom action but that is executed after the uninstall of the previous install.

Is there a way to determine weather the uninstall is being called by a newer install or because the user chose to uninstall the application?

Thanks