Xenon vented to space

[DocMike]

KSP Version: v1.5.1.2335 Windows 64-bit, new

What Happens: Opening a previously closed xenon tank results in instant depletion of said tank.

Mods / Add-Ons: All Stock

Steps to Replicate: 

Launch any ship with ion propulsion and (in my case) two X-750 tanks

Close one of the tanks to keep fuel reserve.

Spend any xenon from the other tank

Reopen the tank

Xenon content in said tank drops instantly from 5700 to zero

[OHara]

Somebody mentioned something similar a couple weeks ago, version 1.5.0, and posted on the bug tracker.  
That was with LFO tanks, and only happened intermittently, maybe the information helps you avoid the problem.

Quote

 

https://bugs.kerbalspaceprogram.com/issues/20267
Fuel disappearing when locking and unlocking tanks really fast
"How to reproduce: take the fuel tank and start locking and unlocking the tank really fast. See this clip for reference: https://clips.twitch.tv/CaringPlacidAlbatrossPraiseIt"

[Cavscout74]

I've encountered the same issue with some monoprop tanks in 1.5.1.

[swjr-swis]

This is specifically mentioned as being fixed with the upcoming 1.6 patch:

On 11/21/2018 at 10:47 PM, SQUAD said:

and we also fixed an issue that drained the fuel from tanks when the fuel availability icon was double-clicked.

[Kerbinchaser]

Sounds like an Apollo 13 kinda thing. It actually sounds pretty cool, adding a new degree of difficulty to the game. Of course, I see how it could get annoying.  

[PhoenixRise86]

This bug has been screwing up my Jool 5+ mission with terrible aggravation. It needs to be stopped. Hoping careful clicking and leaving alone will fix it.

[swjr-swis]

This bug should be fixed in 1.6.0, according to the release notes:

Quote

* Fix fuel being drained from tanks when fuel availability icon is double-clicked.