When I undo a paragraph tab stop action, like adding a tab or moving its position - it takes about a second for the rulers to reflect this action. This is on a machine which is not under heavy load, with plenty of free RAM, with 4 cores etc and when otherwise the UI is pretty responsive. This is in stark contrast to the original action, which, if performed using the ruler, seems instantaneous.
Seeing the same thing with the action of setting a first-line indent. Even with an empty Writer document.