You can set a preference for your account to choose "enabled on last row" which copies/duplicates the last row, or "enable on all rows", which allows copying of any row to the last row in a dynamic matrix.
1. Go to Setup > Customization Preferences.
2. Type "Copy" in the Search field.
3. In the Term field, type the appropriate choice.
- 0 = Disabled
- 1 = Enabled Copying Last Row Only
- 2 = Enable Copying All Rows