I found one question in Microsoft Dynamics CRM Forum today, which seems like a bug in CRM 2015, because I am not able to replicate this issue in CRM 2013. This issue comes when opportunity is created as system calculated without using price list. So when we will create opportunity record and fill revenue option as ‘System Calculated’ and won’t select any price list, after saving opportunity record, it will still display ‘unsaved changes’ under task bar like following screenshot:

And if you will try to close this record it will display alert regarding unsaved changes. Quick workaround to fix this issue is to fill price list field, so if we will opportunity record with price list selected and revenue filled as system calculated and will save record, we won’t get this issue.