Entering the exact time of a maneuver node in the UT text box moves the node around the proposed maneuver instead around the current orbit.
KSP 1.8.1 (No Mods)
How to replicate:
1. Load 'Movement Node Bug Quicksave.sfs'
2. Go to Map Mode
3. Click on node to open maneuver node tab at the bottom left
4. Change UT from the clock (Y D H M S is broken) to S (seconds)
5. Enter 3000
Before.png and After.png will show what happens.
Go to the gizmo and move the node around with the right and left arrow