Spurious torque

[jj314]

The attached craft should have zero torque. Yet, KER shows 0.01 kNm. Maybe a floating point round off error?

To reproduce simply place an S4-512 Fuel Tank and attach 4 vector engines using 4 way symmetry on the bottom. Or load the craft file: https://pastebin.com/Y1mMvEbq

Note, that while 0.01 seems like an insignificant amount, this is just a minimal example. I have a larger craft where the errors add up to significant amounts.