FYI, i know this is old, but moveEditorOnEnter is probably what you're looking for. Unfortunately, there is no similar property for tab, but you can look at the code where moveEditorOnEnter is used in the ExtJS source and replicate the functionality for tab as well.
Code:
onEditorKey : function(field, e){ var k = e.getKey(),
newCell,
g = this.grid,
last = g.lastEdit,
ed = g.activeEditor,
shift = e.shiftKey,
ae, last, r, c;
if(k == e.TAB){
e.stopEvent();
ed.completeEdit();
if(shift){
newCell = g.walkCells(ed.row, ed.col-1, -1, this.acceptsNav, this);
}else{
newCell = g.walkCells(ed.row, ed.col+1, 1, this.acceptsNav, this);
}
}else if(k == e.ENTER){
if(this.moveEditorOnEnter !== false){
if(shift){
newCell = g.walkCells(last.row - 1, last.col, -1, this.acceptsNav, this);
}else{
newCell = g.walkCells(last.row + 1, last.col, 1, this.acceptsNav, this);
}
}
}
if(newCell){
r = newCell[0];
c = newCell[1];
this.onEditorSelect(r, last.row);
if(g.isEditor && g.editing){
ae = g.activeEditor;
if(ae && ae.field.triggerBlur){
ae.field.triggerBlur();
}
}
g.startEditing(r, c);
}
},