Why is fuel flowing across an inline decoupler?

[podbaydoor]

I've got a space plane and probe both burning LF/O. I designed the plane so it burns through all its fuel just before making orbit, and switches to monoprop engines for the last few m/s. When I go to deploy the probe, I find the plane has burnt through the probe's LF/O. I had "disable crossfeed" set in the SPH (it's disabled, so "enable crossfeed" is what's displayed. Messing with priority won't solve things here because the plane will attempt to burn all available fuel. I just need to isolate the probe, and it seems like the crossfeed rules are being ignored.

This doesn't happen on rockets for some reason. On rockets I don't need to mess with fuel flow or crossfeed rules at all. It works out of the box as I would expect.

Anyone else seeing this? Is there another setting I need to mess with?  A mod? Does root part matter?

KSP 1.2.2

Edited April 19, 2017 by podbaydoor

[bewing]

As a workaround, you can lock the fuel tanks on the probe before launching.

 

[Spricigo]

It don't seem to be working how it should be.  Checklist :

>crossfed disabled? 

>probe's engine off the whole time? 

>are you sure there was more fuel in probe's tanks? 

>mode affecting fuel flow? 

>other mod issues? 

[podbaydoor]

3 hours ago, bewing said:

As a workaround, you can lock the fuel tanks on the probe before launching.

 

Figured that out and seems to work. Still not the behavior I expect though.

2 hours ago, Spricigo said:

It don't seem to be working how it should be.  Checklist :

>crossfed disabled? 

>probe's engine off the whole time? 

>are you sure there was more fuel in probe's tanks? 

>mode affecting fuel flow? 

>other mod issues? 

Crossfeed is disabled at takeoff, probe's engine is disabled, probe's tanks are full. Not sure why you mean by "mode". I have Kerbalism and CRP installed which I know provide lots of fuel flow behavior definitions, but none of those should be interfering with the stock LF/Ox behavior.

[Spricigo]

was a typo, meant to be 'mod affecting fuel flow'

No other ideas about what should you check. But nice to know locking resource is a viable workaround even if its not the best solution.

 

[FullMetalMachinist]

9 hours ago, podbaydoor said:

I have Kerbalism and CRP installed which I know provide lots of fuel flow behavior definitions, but none of those should be interfering with the stock LF/Ox behavior.

Careful about making that assumption. I've seen lots of mods effect the game in ways that were completely unrelated to what the mod was supposed to do. 

I would load an unmodded game and launch your ship, see if you can reproduce it in stock.