Kerbal Space Program

What happens:

The calculated deltaV values on crafts with liquid side boosters that are connected via fuel ducts to the central liquid stage gets calculated very wrongly when flow priority on one of multiple side liquid fuel tanks is changed.

Steps to reproduce:

• enable "advanced tweakables" setting
• build or load the craft in the VAB or SPH
• change the flow priority on the bottom side fuel tanks by 1 and observe how the deltaV on both stages changes even though it shouldn't change at all

Craft description (in case the craft file doesn't work):

• command module
• liquid fuel (and oxidizer) tank below command module
• two radial decouplers on the sides of the tank
• two fuel tanks on each decoupler (needs to be multiple!)
• attach an engine to the bottom of each fuel tank stack (a total of three)
• put FTX-2 External Fuel Ducts from the top side tanks to the central tank
• ensure that the staging is as in the screenshots: * stage 1 with all engines * stage 0 with decouplers
• positive deltaV should be shown for each stage
• change (increase or decrease) the flow priority on one of the side tanks by 1
• The deltaV on stage 1 drops a lot and the deltaV of stage 0 drops to zero. This is the bug.

Note:
The deltaV also gets calculated when the craft is launched, but once the boosters are separated the deltaV gets calculated correctly.

Version information:

• Linux steam version 1.6.0
• without steam running
• launched by running KSP.x86_64 from the terminal

System specifications:

• Arch Linux Kernel 4.19.10-arch1-1-ARCH x86_64
• Intel i5-6200U CPU
• integrated graphics