Unrequested text defaulting

Hello *, we have pointed out an unrequested behaviour within transaction processing after upgrade CRM. 1. Maintenance of an activity containing a text (note) 2. Save activity 3. Create single opportunity --> The text (note) of the activity is transferred automatically (no such customizing performed!) to the opportunity. It seams like a buffer Topic or something like this. We cleared browser Cache and invalidated Server Cache in tx SMICM. Any ideas? Kind regards Thomas