Quoting Mo :
"We do need a way to link the four values (Jasper also mentioned it a few months ago) but I'm not sure it's right to assume the users intentions based on input in the first field. Certainly not a fan of switching between a single/multiple field mode, I prefer the editor to look consistent so it is familiar and recognisable.

How about adding some simple UI? The proposal below allows the user to edit all fields independently and has a button to copy the value of the first field into the others. This button is deliberately placed after the first field allowing quick keyboard inputs to copy the values."
See attached screenshot.