It's happening on multiple engines from this mod, at least the ones I tested (MATTOCK, ESTOC, and Aerospike, and presumably others). If you lock a tank in the SPH/VAB, when you unlock the tank in-flight the engines will instantly drain the tank completely. I'm using 1.8.3.4, testing it (along with dependencies) on an otherwise stock install of KSP 1.5.
It's happening on multiple engines from this mod, at least the ones I tested (MATTOCK, ESTOC, and Aerospike, and presumably others). If you lock a tank in the SPH/VAB, when you unlock the tank in-flight the engines will instantly drain the tank completely. I'm using 1.8.3.4, testing it (along with dependencies) on an otherwise stock install of KSP 1.5.