here is the setup:
1. place the dispenser.

(make sure the dispenser faces the outside of the border)

2. put a boat in the dispenser

3. place water on top of the dispenser

4. quickly place a button and press it

5. enter the boat

you are now able to explore outside of the worldborder(works in survival)

I believe this is a bug because the worldborder should keep players in.

this can be used as a exploit in servers if the owner set up the border in such a way that it prevents players from coming into areas they don't intend you to be.