From a little messing around, it looks like jump distance for the Navigation UI Panel is calculated using the mass of your ship when you entered the system. (including cargo and equipment) and is NOT UPDATED when your ship's mass changes.
The Galaxy Map navigation tab will show you the correct information, but you might need to exit the game and restart for the Navigation UI to allow you to select a destination.
The Galaxy Map navigation tab will show you the correct information, but you might need to exit the game and restart for the Navigation UI to allow you to select a destination.