I created a plane powered by two Wheesley engines attached to engine nacelles (craft file). I was going to be traveling a ways so I added some fuel tanks as well, but I didn't realize there had to be fuel lines to route the fuel to the engines. I'd already launched when I noticed this, so I thought oh well I'll keep going until the nacelles run out anyways.
Much to my surprise the plane kept flying even with the engine nacelles empty and with the fuel gauge showing a steady 800 units of liquid fuel left. It seems like the plane slowed down at that point (to ~170 m/s) but I don't understand why the engines kept working at all with no fuel. Am I missing something?
Here are the plugins I have installed in case they're relevant somehow:
KerbalAlarmClock
Docking Port Alignment Indicator
KerbalEngineer
EditorExtensions
WaypointManager