Every pump I've ever tried it with will 'dribble' a shell or fired hull out of the ejection port if you just s l o w l y open the bolt.
There's no spring loaded ejector sufficiently strong to kick the shell out, ejection depends on the force imparted by the extractor dragging the shell back into the ejector and pivoting it out of the ejection port.
It's a feature, not a bug...
Pump it firmly - ONE count all the way back till the bolt stops, then count TWO all the way forward till it stops. If you will always think 'ONE stop TWO stop' as you run the gun, you will never short stroke it.
Mindset - Skillset - Toolset. In that order!
Attitude and skill will get you through times of no gear, better than gear will get you through times of no attitude and no skill.