i don't have that problem with my 835 , in mine , the spent shell is ejected before the loading arm ( don't know the proper name ) drops to let a new shell enter the loading port of the receiver , then once the loading arm has the shell into the receiver it rises back up and acts kind of like a guide so the loaded shell can't fall out of the receiver ,

the only thing that i could even remotely think of that could cause that would be your magazine spring haveing too much stress on it , like too many shells in the magazine , or just simply the magazine spring being to strong that it pushes the shells back with enough force that they go into the receiver to speedily and spill out. or some kind of loading bar defect
best to take it to a gun smith as i can only guess