mrkgnao: Tried again with Jill just now. Got the same problem as before. I believe it depends on your last cart.
Could you please try this:
1) Put a game you do not own in your cart.
2) Select Paypal as your payment option.
3) Remove the game from your cart without buying it.
4) Add Jill to your cart.
5) Type the gift recipient's address.
6) Try checking out. Did you see the issue or not?
7) Ask GOG to add an option to delete unwanted gifts from your order history (optional).
Sorry for the late reply.
That's interesting, especially since I didn't, and still don't, own
Jill of the Jungle: The Complete Trilogy when I did the test, i.e. requirement of step 1 was fulfilled (I think?).
Do you think that makes a difference regarding my test result, or do you still think I should try the above steps, i.e. game of steps 1-3 mustn't be a free one?