its normal?f.e. in blitz behind the walls
there's always one last paintball that takes awhile to get out. It also goes higher in the air causing that to solve both of yours because A) it can shoot over the wall and B) because it goes higher in the air it takes longer than the rest to come down.
There's a feature vote for decreasing the explosion radius of grenades, but most people seem to be against it. Not sure what other changes would "improve" it. It shoots paint in random directions, and that's about all there is to it.
I think shortening the time that it actually emits balls for (or lengthening the sound) would solve what most people perceive the problem to be.