Greetings,
We’ve been able to confirm this unintended behavior and Development has been alerted. Unfortunately, in the interim, there’s no setting to change that would stop EndNote from automatically launching when starting Word 2008 or Word 2011. Reverting back to EndNote X7.4 would temporarily resolve the issue, but you’d lose Word 2016 support and the other benefits that EndNote X7.5 provides - please contact Technical Support if you’d like assistance related to reinstalling EndNote X7.4. Otherwise, our developers are actively investigating and we’ll let everyone know once resolution has been reached. We do apologize for any inconvenience caused by this situation.