Stock delta-v tool showing double mass at random times

[Levfendi]

I have a modded install (1.12.2) with a few mods such as Snacks, Kerbal Construction Time, and Scrap Yard. I have stock planets and no physics-changing mods like FAR or RO. I have the strangest bug that occurs both in flight and in the VAB: Sometimes the dV tools assume that the mass of the entire stage is different from what it actually is (usually double). I figured out the root of the problem is to do with mass because "starting mass" is the thing that is obviously incorrect and it leads to incorrect TWR and dV calculations while Isp behaves as expected. I think the mass value is the issue because when the bug occurs in VAB, I can clearly see that the engineering report vessel mass and the first stage burn's starting mass are different (usually doubled). I am 99% sure it is only the displayed numbers that are wrong and the actual numbers are alright because I can take off with "0.6" TWR and reach LKO with "2000" dV. In VAB, removing and re-adding all the non-root parts fixes the issue by refreshing the calculation and in flight, reverting to launch sometimes corrects the issue. 

I verify the game files frequently and there tends to be more than a few to reinstall each time, but even right after that the bug can occur. I think I'll install Kerbal Engineering Redux to compare values and maybe ignore stock calculations entirely but I wanted to post about this bug here too because I cannot believe no one has come across it before. Anyone?

[jimmymcgoochie]

You’ve put mods into the Steam copy of KSP, haven’t you… Don’t do that. Steam breaks stuff with modded KSP all the time.

To fix this problem in the long run:

1. Copy your saves (right click KSP in Steam library > browse local files, your saves are in the saves folder) and paste to desktop. If you use CKAN, create a modpack from what you have installed (File > export modpack).
2. Disable Steam cloud syncing for KSP (right click KSP in Steam library > properties).
3. Completely uninstall KSP through Steam.
4. Reinstall KSP through Steam, pick the version you want (e.g. 1.11.2) and verify game files once it’s done.
5. Copy the entirety of KSP out of Steam/steamapps/common and paste it somewhere else e.g. desktop, then rename it to something you’ll remember.
6. Install mods into this copy (manually or via the CKAN modpack you made earlier) and copy your saves over to this new copy.
7. That’s it- you should now be able to play KSP without any further weirdness in stock systems, though if you add/remove/change/update mods things may still go wrong; that’s just mods for you.