Are you still using that tried and tested copy and paste to get text from one of the proposals into the New Version edit field?
Why not simply double-click the header of the proposal?
Or, if you prefer to keep your hands to the keyboard, use a shortcut.

The "Shortcuts" tab of the "Preferences" dialog lists all modifiable shortcuts.
So, if you find one of the shortcuts hard to remember, change it to the combination of your liking.

Suppose you want "Alt-Right Arrow" as the shortcut to take you to the next sentence.
Click the "Next sentence" row and press your new key combination. Then click the "Change" button.
If the new combination is already in use, Tstream Editor Studio will warn you and you'll have to choose a different shortcut. When you're done, click "OK" to close the dialog and save your changes.

Note that the combination of arrows and the Ctrl-key won't work as they are reserved by the edit field.

Next time: change the sentence colors.