Thanks for your comment and question! We are considering doing a third mode that can swap the order, so you can freely drag your drawings around.
The way Slide mode works is that the order of your drawings are always the same, you use it for adjusting the local timing without messing up timing later down the timeline. So let’s say you have key drawings laid out in sync with an audio track. Then you can, in slide mode, adjust your individual drawing up or down to hit the exact beats in your audio track, without changing your perfect sync/timing of your drawings later in your animation.
It is deliberate that you can’t (accidentally) drag a key drawing to the other side of its neighbour key.
But, as you request, sometimes it would be very relevant to be able to do so. 😉