just finishing up a kerpallo 2 (kerpallo 1 failed with not enough boosters) flight with almost all stock parts (only mod part is a stronger nuclear engine that has no gimball, 300 thrust, 5 burn rate, and a minimum of 30 thrust)
Everything looked good, got into orbit, set up intercept with the mun, began burn to get there.
Still had some fuel left so the engine kept burning, and I had to eject the stage or I'd overshoot and leave kearth
I separate stages, but I didn't have enough force, so the nuclear stack pushed my liquid engine. I couldn't risk lighting the detached stage, so I turned the nose down to let the nuclear stage keep going off to the sun, but it clipped my guiding wing/strut and broke off the stage's liquid engine.
I thought they were lost in orbit, until I realized I had sever RCS thrusters which might do the trick.
I warped to apoge, then set all the RCS thrusters to reverse thrust to slow me down enough that my orbit would put me in atmo, and it just barely worked, nearly ran into the Mun as well